Structure, Bonding, and Reactivity of Binuclear Complexes Having

4384

Organometallics 2010, 29, 4384–4395 DOI: 10.1021/om100529a

Structure, Bonding, and Reactivity of Binuclear Complexes Having Asymmetric Trigonal Phosphinidene Bridges: Addition of 16-Electron Metal Carbonyl Fragments to the Dimolybdenum Compounds [Mo2Cp(μ-K1:K1,η5-PC5H4)(CO)2L] and [Mo2Cp2(μ-PH)(CO)2L] (L = η6-1,3,5-C6H3tBu3)§ M. Angeles Alvarez, Inmaculada Amor, M. Esther Garcı´ a, Daniel Garcı´ a-Viv o, Miguel A. Ruiz,* and Jaime Suarez Departamento de Quı´mica Org anica e Inorg anica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain Received May 28, 2010

The phosphinidene-bridged complexes [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2L] and [Mo2Cp2(μ-PH)(CO)2L] (Cp = η5-C5H5; L = η6-1,3,5-C6H3tBu3) react readily with [Fe2(CO)9] or the solvate complexes [M(CO)5(THF)] (M=Cr, Mo, W; THF=tetrahydrofuran) to give, as a result of the addition of the corresponding 16-electron M(CO)n fragments to their multiple Mo-P bonds, the trinuclear derivatives [FeMo2Cp(μ3-κ1:κ1:κ1,η5-PC5H4)(CO)6L], [MMo2Cp(μ3-κ1:κ1:κ1,η5-PC5H4)(CO)7L][FeMo2Cp2(μ3-PH)(CO)6L], and [MMo2Cp2(μ3-PH)(CO)7L]. The PH-bridged complexes display a distorted tetrahedral environment around their P atom, according to X-ray diffraction studies on the Fe, Cr, and W compounds, whereas the PC5H4-bridged ones display an unusual trigonalpyramidal geometry around the P atoms (sum of M-P-M angles 359.6° for the Fe compound). The latter species were stable toward hydrolysis, whereas the trinuclear PH-bridged complexes underwent easy hydrolysis of their P-Mo(metallocene) bonds to give the corresponding PH2-bridged derivatives [FeMoCp(μ-PH2)(CO)6L] and [MMoCp(μ-PH2)(CO)7L] (M=Cr, Mo, W).

Introduction The chemistry of complexes containing multiple bonds between metals and main-group elements is a fascinating field in contemporary chemistry, and these species are excellent starting materials for the synthesis of unusual ligands that are stabilized by the protective coordination sphere of the metal complex.1 In this context, the chemistry of transition-metal complexes having phosphinidene ligands § This paper is dedicated to the memory of Dr. J. Manuel Concellon, former dean of the School of Chemistry and distinguished professor of organic chemistry at the Universidad de Oviedo. *To whom correspondence should be addressed. E-mail: mara@ uniovi.es. (1) (a) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy; Wiley: New York, 1998. (b) Johnson, B. P.; Balazs, G.; Scheer, M. Top. Curr. Chem. 2004, 232, 1. (c) Balazs, G.; Gregoriades, L. J.; Scheer, M. Organometallics 2007, 26, 3058. (d) Cummins, C. C. Angew. Chem., Int. Ed. 2006, 45, 862–870. (e) Weber, L. Angew. Chem., Int. Ed. 2007, 46, 830–832. (2) Reviews: (a) Aktas, H.; Slootweg, J. C.; Lammerstma, K. Angew. Chem., Int. Ed. 2010, 49, 2. (b) Waterman, R. Dalton Trans. 2009, 18. (c) Mathey, F. Dalton Trans. 2007, 1861. (d) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95. (e) Streubel, R. Top. Curr. Chem. 2003, 223, 91. (f) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578. (g) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127. (h) Mathey, F.; Tran-Huy, N. H.; Marinetti, A. Helv. Chim. Acta 2001, 84, 2938. (i) Stephan, D. W. Angew. Chem., Int. Ed. 2000, 39, 314. (j) Shah, S.; Protasiewicz, J. D. Coord. Chem. Rev. 2000, 210, 181. (k) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9. (l) Cowley, A. H. Acc. Chem. Res. 1997, 30, 445. (m) Cowley, A. H.; Barron, A. R. Acc. Chem. Res. 1988, 21, 81. (n) Huttner, G.; Knoll, K. Angew. Chem., Int. Ed. 1987, 26, 743. (o) Huttner, G.; Evertz, K. Acc. Chem. Res. 1986, 19, 406.

pubs.acs.org/Organometallics

Published on Web 09/14/2010

(PR, with R = alkyl, aryl, etc.) has undergone a great and exciting development over the last years.2 Many of the results in this field have been rationalized on the basis of the diagonal relationship linking phosphorus to carbon. For instance, the isolobal connection between PR and CR2 fragments explains the analogies found between terminal bent-phosphinidene complexes and carbene complexes. Actually, these phosphinidene complexes can be analogously classified as either electrophilic or nucleophilic, depending on the nature of the metal fragments to which these ligands are bound.2d,g,h In a simplified way, the metal-phosphorus bonding in these phosphinidene complexes approaches the extreme descriptions of single-dative and double bonds, respectively (A and B in Chart 1), while the high reactivity of these molecules arises from the presence of both the multiple M-P bond and the lone electron pair at phosphorus, coupled to the availability in both cases of a lowenergy, P-centered LUMO. The phosphinidene ligand, however, is an extremely versatile four-electron donor that can bind efficiently up to four metal atoms in many other ways (C to H in Chart 1), and the nature of the M-P bond changes dramatically among these coordination modes. For instance, the M-P bonds in the μ3- or μ4-bridging modes are essentially single, so little reactivity is expected for them and, indeed, PR groups are good (and relatively inert) supporting ligands for metal clusters, although some insertion reactions into their M-P bonds have been reported.2n,3 Within this group, moreover, we note that those species bridged by the phosphinidene (PH) ligand are the least studied ones.4 r 2010 American Chemical Society

Article

In contrast to the above state of facts, the chemistry of binuclear complexes having phosphinidene bridges has remained comparatively little explored until recently, even though the presence of multiple M-P bonds or lone pairs at phosphorus in their different coordination modes (D to F in Chart 1) should make these complexes quite reactive toward unsaturated organic molecules or other metal complexes.5,6 Recent work from our lab,5a,7 and the group of Carty,6e,f,h has shown that this is indeed the case for several complexes displaying symmetrical phosphinidene bridges of type D, but the chemistry of asymmetric complexes of type E remains essentially unexplored.8 Then, following our recent discovery of new and unusual complexes of this type such as the arylphosphinidene complex [Mo2Cp2(μ-κ1:κ1,η6-PMes*)(CO)2],9 the (3) For recent work on cluster complexes having μ3- and μ4-PR ligands see: (a) Sanchez-Cabrera, G.; Leyva, M. A.; Zuno-Cruz, F. J.; Hernandez-Cruz, M. G.; Rosales-Hoz, M. J. J. Organomet. Chem. 2009, 694, 1949. (b) Shima, T.; Sugimura, Y.; Suzuki, H. Organometallics 2009, 28, 871. (c) Bott, S. G.; Shen, H.; Huang, S. H.; Richmond, M. G. J. Organomet. Chem. 2008, 693, 2327. (d) Adams, R. D.; Boswell, E. M.; Captain, B.; Zhu, L. J. Cluster Sci. 2008, 19, 121. (e) Andrews, C. D.; Burrowa, A. D.; Green, M.; Lynam, J. M.; Mahon, M. F. J. Organomet. Chem. 2006, 691, 2859. (f) Kakizawa, T.; Hashimoto, H.; Tobita, H. J. Organomet. Chem. 2006, 691, 726. (g) Deeming, A. J.; Forth, C. S.; Hyder, M. I.; Kabir, S. E.; Norlander, E.; Rodgers, F.; Ullmann, B. Eur. J. Inorg. Chem. 2005, 4352. (h) Scoles, L.; Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Inorg. Chem. 2005, 44, 2766. (i) Zhong, X.; Ang, S. G.; Ang, H. G. J. Organomet. Chem. 2004, 689, 361. (4) PH-bridged polynuclear complexes: (a) Ebsworth, E. A. V.; McIntosh, A. P.; Schr€ oder, M. J. Organomet. Chem. 1986, 312, C41. (b) Cardin, C. J.; Colbran, S. B.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R. J. Chem. Soc., Chem. Commun. 1986, 1288. (c) Johnson, B. F. G.; Lewis, J.; Norlander, E.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1996, 755. (d) Fl€ orke, U.; Haupt, H. J. Acta Cryst. Sect. C 1997, 53, 876. (e) Davies, J. E.; Mays, M. J.; Pook, E. J.; Raithby, P. R.; Tompkin, P. K. J. Chem. Soc., Dalton Trans. 1997, 3283. (f) Sekar, P.; Scheer, M.; Voigt, A.; Kirmse, R. Organometallics 1999, 18, 2833. (g) Borg-Breen, C. C.; Bautista, M. T.; Schauer, C. K.; White, P. S. J. Am. Chem. Soc. 2000, 122, 3952, and references therein. (h) Vogel, U.; Sekar, P.; Ahlrichs, R.; Huniar, U.; Scheer, M. Eur. J. Inorg. Chem. 2003, 1518. (5) (a) Amor, I.; Garcı´ a, M. E.; Ruiz, M. A.; Saez, D.; Hamidov, H.; Jeffery, J. C. Organometallics 2006, 25, 4857, and references therein. (b) Alvarez, C. M.; Alvarez, M. A.; García, M. E.; Gonzalez, R.; Ruiz, M. A.; Hamidov, H.; Jeffery, J. C. Organometallics 2005, 24, 5503. (c) Alvarez, M. A.; García, M. E.; Gonzalez, R.; Ruiz, M. A. Organometallics 2008, 27, 1037. (6) For recent work on binuclear phosphinidene complexes, see: (a) Stubenhofer, M.; Kuntz, C.; Balazs, G.; Zabel, M.; Scheer, M. Chem. Commun. 2009, 1745. (b) Scheer, M.; Himmel, D.; Kuntz, C.; Zhan, S.; Leiner, E. Chem.;Eur. J. 2008, 14, 9020. (c) Cui, P.; Chen, Y.; Xu, X.; Sun, J. Chem. Commun. 2008, 5547. (d) Masuda, J. D.; Jantunen, K. C.; Ozerov, O. V.; Noonan, J. T.; Gates, D. P.; Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2008, 130, 2408. (e) Graham, T. W.; Udachin, K. A.; Carty, A. J. Inorg. Chim. Acta 2007, 360, 1376. (f) Graham, T. W.; Udachin, K. A.; Carty, A. J. Chem. Commun. 2006, 2699. (g) Bai, G.; Pingrong, W.; Das, A. K.; Stephan, D. W. Dalton Trans. 2006, 1141. (h) Graham, T. W.; Udachin, K. A.; Carty, A. J. Chem. Commun. 2005, 4441. (i) Shaver, M. P.; Fryzuk, M. D. Organometallics 2005, 24, 1419. (j) Driess, M.; Aust, J.; Merz, K. Eur. J. Chem. 2005, 866. (k) Scheer, M.; Vogel, U.; Becker, U.; Balazs, G.; Scheer, P.; H€ onle, W.; Becker, M.; Jansen, M. Eur. J. Chem. 2005, 135. (l) SanchezNieves, J.; Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Can. J. Chem. 2004, 82, 1507. (m) Termaten, A. T.; Nijbacker, T.; Ehlers, A. W.; Schakel, M.; Lutz, M.; Spek, A. L.; McKee, M. L.; Lammertsma, K. Chem.;Eur. J. 2004, 10, 4063. (n) Sanchez-Nieves, J.; Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Inorg. Chim. Acta 2003, 350, 486. (o) Blaurock, S.; Hey-Hawkins, E. Eur. J. Inorg. Chem. 2002, 2975. (7) (a) Garcı´ a, M. E.; Riera, V.; Ruiz, M. A.; Saez, D.; Vaissermann, J.; Jeffery, J. C. J. Am. Chem. Soc. 2002, 124, 14304. (8) Asymmetric μ2-PR complexes: (a) Malisch, W.; Hirth, U. A.; Bright, T. A.; K€ ab, H.; Ertel, T. S.; H€ uckmann, S.; Bertagnolli, H. Angew. Chem., Int. Ed. Engl. 1992, 31, 1525. (b) Hirth, U. A.; Malisch, W. J. Organomet. Chem. 1992, 439, C16. (c) Lang, H.; Winter, M.; Leise, M.; Walter, O.; Zsolnai, L. J. Chem. Soc., Chem. Commun. 1994, 595. (d) Hirsekorn, K. F.; Veige, A. S.; Wolczanski, P. T. J. Am. Chem. Soc. 2006, 128, 2192. (9) Garcı´ a, M. E.; Riera, V.; Ruiz, M. A.; Saez, D.; Hamidov, H.; Jeffery, J. C.; Riis-Johannessen, T. J. Am. Chem. Soc. 2003, 125, 13044.

Organometallics, Vol. 29, No. 19, 2010

4385

Chart 1

Chart 2

cylopentadienylidene-phosphinidene [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2L] (1),5 and the phosphinidene complex [Mo2Cp2(μ-PH)(CO)2L] (2)10 (Chart 2, Cp = η5-C5H5; Mes* = 2,4,6C6H2tBu3; L = η6-1,3,5-C6H3tBu3) we started a systematic study of their reactivity. First we should consider that all these molecules display a PR group connecting 17- and 15-electron metal fragments, and in such a situation several resonance forms can be used to describe the corresponding Mo-P bonds (three of them shown in Chart 2), which suggests the attractive idea that the reactivity of these multiple Mo-P bonds might be related to that of the double MdC bonds (carbene complexes) or even to that of the triple MtC bonds (carbyne complexes). Preliminary studies on the mentioned aryl- and cyclopentadienylidene-phosphinidene complexes revealed severe steric crowding in the first of these two molecules, it being only able to add relatively small molecules or fragments such as CO, CuCl, or AuCl.5a,11 In contrast, the less congested compound 1 would additionally react with more complex molecules such as alkynes, Fe2(CO)9, and Co2(CO)8.12 As expected, the reactivity of 1 was mainly located at the short (multiple) Mo-P bond, but the reaction products displayed an unusual geometry around the phosphorus atom, to be described as distorted trigonal pyramidal (TP) rather than the more usual tetrahedral geometry. We thus decided to further explore this matter by comparing the reactivity of 1 to that of (10) Amor, I.; Garcı´ a-Viv o, D.; Garcı´ a, M. E.; Ruiz, M. A.; Saez, D.; Hamidov, H.; Jeffery, J. C. Organometallics 2007, 26, 466. (11) Alvarez, M. A.; Amor, I.; Garcı´ a, M. E.; Ruiz, M. A. Inorg. Chem. 2008, 47, 7963. (12) Alvarez, M. A.; Amor, I.; Garcı´ a, M. E.; Garcı´ a-Viv o, D.; Ruiz, M. A. Inorg. Chem. 2007, 46, 6230.

4386


Alvarez et al.

Table 1. Selected Data for the DFT-Optimized Geometries of Complexes 1 and 2a parameter

1b

2

exptl (1)b

Mo1-P Mo2-P P-C/H Mo2-C Mo1-P-Mo2 Mo1-P-C/H Mo2-P-C/H

2.272 2.505 1.807 2.231 165.2 134.8 59.7

2.289 2.592 1.428

2.252(2) 2.403(1) 1.807(6) 2.208(5) 163.7(1) 134.9(2) 61.4(2)

140.3 116.9 102.5

a Bond lengths (A˚) and angles (deg) according to the labeling shown in the figure; see the Experimental Section for details of the DFT calculations.

Figure 1. DFT-optimized structures of compounds 1 (left) and 2 (right), with H atoms (except the one bound to P) omitted for clarity.

Structure and Bonding in the Phosphinidene Complex 2. Comparison with the Cyclopentadienylidene-phosphinidene Complex 1. In our preliminary study,12 we reported the crystal structure of complex 1 and a brief analysis of the bonding in this molecule on the basis of DFT13 calculations. Unfortunately, we have been unable to obtain good-quality crystals of compound 2, even if we have now found that its thermal stability at room temperature is relatively conventional when very pure solutions of the complex are handled under the strict exclusion of air. Then we have carried out DFT calculations for 2 at the same level of theory used for compound 1, in order to compare these two compounds (see the Experimental Section for details). The electronic structure and bonding in these unsaturated molecules have been analyzed through the properties of the relevant molecular orbitals and also by inspection of the topological properties of the electron density, as managed in the AIM theory.14

The most relevant parameters derived from the geometry optimization of compounds 1 and 2 can be found in Table 1, with the corresponding views being collected in Figure 1. The optimized bond lengths for 1 are in reasonable good agreement with the data measured using X-ray diffraction,12 although the computed values for lengths involving the metal atoms tend to be slightly longer (less than 0.05 A˚) than the corresponding experimental data. This is a common tendency with the functionals currently used in the DFT computations of transition-metal compounds.13a,15 The major difference is found in the long Mo2-P distance, overestimated by ca. 0.1 A˚ (Table 1). Yet, the calculations reproduce well the fact that the Mo-P lengths in 1 have intermediate values, with the long Mo-P distance being shorter than the reference single-bond lengths (e.g., 2.555(3) A˚ for the corresponding distance in the asymmetrically bridged [W2Cp2(μ-PMes)(CO)4(PH2Mes)], with Mes =2,4,6-C6H2Me3).8a At the same time, the short Mo1-P distance falls above the range expected for Mo-P triple bonds (e.g., 2.13-2.20 A˚ in the phosphide-bridged compounds [L3WtPfW(CO)5], with L3 = tridentate N- or O-donor ligand)16 and within the range of 2.20-2.30 A˚ displayed by terminal three-electron-donor phosphide ligands (e.g., 2.284(4) A˚ for [WCp(PtBu2)(CO)2]17 or 2.204(1) A˚ for the fluorophosphide complex [MoCp(PFMes*)(CO)2]).18 All of this is suggestive of a substantial delocalization of the Mo-P π-bonding interaction along the Mo-P-Mo chain, in agreement with the nature of the orbitals of the molecule, to be discussed below. The DFT-optimized structure of 2 has two significant differences when compared to that of 1. First, because of the absence of further links (other than the metals) for the PH ligand, the metallocene plane of the MoCpL fragment is rotated by 90° with respect to the plane bisecting the MoCp(CO)2 fragment, surely to minimize the steric repulsions among the different ligands present. Actually, a rotamer of 2 having an “eclipsed” conformation comparable to that of 1 was not found to be a minimum on the energy surface, and the same was found for other rotamers with intermediate conformations. The second difference concerns the Mo2P skeleton, displaying a not so wide Mo-P-Mo angle (ca. 140°) and Mo-P lengths that are respectively slightly (ca. 0.02 A˚) and significantly (ca. 0.09 A˚) longer than the short and long Mo-P distances in 1 (Table 1). Although part of this lengthening can be due to the changes operating in the bond angles, the significant increase of the interatomic separation in the long bond suggests that the Mo-P

(13) (a) Koch, W.; Holthausen, M. C. A Chemist’s Guide to Density Functional Theory, 2nd ed.; Wiley-VCH: Weinheim, 2002. (b) Ziegler, T. Chem. Rev. 1991, 91, 651. (c) Foresman, J. B.; Frisch, ó. Exploring Chemistry with Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, PA, 1996. (14) (a) Bader, R. F. W. Atoms in Molecules-A Quantum Theory; Oxford University Press: Oxford, U.K., 1990.

(15) Cramer, C. J. Essentials of Computational Chemistry, 2nd ed.; Wiley: Chichester, U.K., 2004. (16) Johnson, B. P.; Balazs, G.; Scheer, M. Top. Curr. Chem. 2004, 232, 1. (17) J€ org, K.; Malisch, W.; Reich, W.; Meyer, A.; Schubert, U. Angew. Chem., Int. Ed. Engl. 1986, 25, 92. (18) Alonso, M.; Garcı´ a, M. E.; Ruiz, M. A.; Hamidov, H.; Jeffery, J. C. J. Am. Chem. Soc. 2004, 126, 13610.

b

Data taken from ref 12.

the phosphinidene complex 2, a molecule having an even less protected multiple P-Mo bond and, above all, having a simple phosphinidene ligand free of the geometrical constraints derived from the bifunctional character of the cyclopentadienylidene-phosphinidene ligand. In this paper we analyze the differences in the structure and bonding of compounds 1 and 2 on the basis of DFT calculations, and we also give full details of their reactions involving the addition of 16-electron metal fragments M(CO)n (M=Fe, n=4; M = Cr, Mo, W; n = 5) to the multiple P-Mo bond present is these substrates. As it will be seen, the geometrical constraints of the PC5H4 ligand (compared to the PH ligand) have significant effects at all levels, not only on the nature of the Mo-P bonds in compounds 1 and 2 but also on the structure and hydrolytic behavior of the heterometallic derivatives of these reactive molecules. Incidentally, the latter has allowed us to synthesize several heterometallic derivatives bridged by the simplest phosphanyl (PH2) group.

Results and Discussion

Article


4387

Table 2. Selected Atomic Charges in Complexes 1 and 2a Mulliken

NPA

atom

1

2

1

2

Mo1 Mo2 P C/H

-0.13 -0.22 0.33 -0.21

-0.10 -0.20 0.05 -0.02

-0.41 -0.05 0.63 -0.36

-0.35 0.04 0.21 -0.01

a Labeling according to the footnote figure in Table 1; see the Experimental Section for details of the DFT calculations.

Figure 2. Selected molecular orbitals of compounds 1 (left) and 2 (right), with their energies (in eV) and main bonding character indicated below.

π-bonding interaction in 2 might be more localized on the short Mo-P bond, in agreement with the nature of the orbitals computed for this molecule. The frontier molecular orbitals of compounds 1 and 2 are depicted in the Figure 2, along with their associated energy and bonding character. The most significant difference between these two molecules concerns the Mo-P π-bonding interaction, as anticipated by the geometrical parameters just discussed. In compound 1, such an interaction is mainly described by the HOMO-1, localized on the short Mo-P bond, and the HOMO-4, delocalized over the Mo-P-Mo

skeleton. Moreover the LUMO is the antibonding counterpart of the HOMO-1, and this pair thus resembles the characteristic frontier orbitals of the double bonds. All of this suggests that at least the forms B and C in Chart 2 are needed to describe the bonding in 1, while the form A possibly has only a minor contribution to the ground-state structure of the complex. In contrast, the Mo-P π-bonding interaction in compound 2 (HOMO-4) is essentially located on the short Mo-P bond, while the LUMO is again the antibonding counterpart of this interaction. Possibly this localizing effect on the π-bonding interaction in 2 is just a geometrical consequence of the rotation of the metallocene plane with respect to the “eclipsed” conformation mentioned above, this destroying the positive overlap with the metallocene fragment. In any case, we conclude that the ground-state electronic structure of compound 2 can be adequately described by just the canonical form B, implying an essentially double Mo-P bond with the 15-electron metal fragment and being therefore comparable to the metal-phosphorus interaction expected for a terminal three-electron-donor PR2 ligand. In spite of this, the atomic charges computed for 2 are similar to those computed for 1 (Table 2), except for some reduction of the positive charge at the P atom, mainly due to the replacement of carbon by the less electronegative H atom. The differences in the electronic distribution in complexes 1 and 2 are, however, properly reflected in significant changes of the electron density (F) at the corresponding Mo-P bond critical points (Table 3), which for compound 2 is increased at the short bond (0.654 e A˚-3) and reduced at the long bond (0.441 e A˚-3), when compared to the values computed for 1, in agreement with the mentioned localization of the π-bonding interaction. Although there are almost no data on related compounds to be used as a reference, these figures are lower than those computed at the same level of theory for the short and long Mo-P bonds in the phosphidebridged complex [Mo2Cp2(μ-P)(CO)2L]þ (0.738 e A˚-3, 2.199 A˚; 0.595 e A˚-3, 2.381 A˚).10 We must note that in this cation one of the π components of the triple Mo-P bond is substantially delocalized along the Mo-P-Mo chain much as found for 1, thus yielding in that case Mo-P bond orders formally lower than three and higher than one, respectively. As a reference for strong single Mo-P bonds (having some dative character) we can also quote the values of ca. 0.53 e A˚-3 for the PCy2-bridged complexes [Mo2Cp2(μ-PCy2)(μ-X)(CO)2] (X = COMe, H, Me, Ph).19 In summary, the values of the electron density at the Mo-P bonds in 2 are also consistent with an almost complete localization of the π-bonding Mo-P interaction on the bond involving the 15-electron metal fragment, and they can be taken as reference figures for double and single Mo-P bonds, respectively. (19) (a) Garcı´ a, M. E.; Garcı´ a-Viv o, D.; Ruiz, M. A.; Alvarez, S.; Aull on, G. Organometallics 2007, 26, 5912. (b) García, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Marchio, L. Organometallics 2007, 26, 6197.

4388


Alvarez et al.

Table 3. Topological Properties of the Electron Density in Complexes 1, 2, and 6aa 1

2

6a

bond

F

rF

F

Mo1-P Mo2-P M-P H/C-P

0.627 0.473

5.21 2.14

0.654 0.441

4.49 1.56

1.040

1.49

1.071

-5.01

2

rF 2

F

r2F

0.516 0.378 0.333 1.086

2.31 1.62 1.79 -3.81

a

Values of the electron density at the bond critical points (F) are given in e A˚-3; values of the laplacian of F at these points (r2F) are given in e A˚-5; labeling according to the footnote figure in Table 1; see the Experimental Section for details of the DFT calculations.

Scheme 1

Scheme 2

Addition of 16-Electron Metal Fragments M(CO)n to Compounds 1 and 2. The multiple P-Mo bond in complexes 1 and 2 is basic enough to act as a donor toward unsaturated metal fragments of type M(CO)n, such as Fe(CO)4 and M(CO)5 (M = Cr, Mo, W), then providing a rational route to heterometallic species bridged by PR ligands. Thus compound 1 reacts smoothly with [Fe2(CO)9] at 273 K to give the trinuclear derivative [FeMo2Cp(μ3-κ1:κ1:κ1,η5-PC5H4)(CO)6L] (3) in good yields, and a similar reaction takes place with the tetrahydrofuran adducts [M(CO)5(THF)], to give the corresponding trinuclear derivatives [MMo2Cp(μ-κ1:κ1: κ1,η5-PC5H4)(CO)7L] (M=Cr (4a), Mo (4b), W(4c); Scheme 1), although the reaction is now almost instantaneous at room temperature when using dichloromethane as solvent. Compound 2 reacts analogously with [Fe2(CO)9] and with the adducts [M(CO)5(THF)] to give the corresponding derivatives

Figure 3. ORTEP diagram (30% probability) of compound 3, with H atoms and tBu groups omitted for clarity.

[FeMo2Cp2(μ3-PH)(CO)6L] (5) and [MMo2Cp2(μ3-PH)(CO)7L] (M = Cr (6a), Mo (6b), W (6c); Scheme 2), but in this case tetrahydrofuran-toluene (Fe) or toluene (Cr-W) was used as reaction solvent to minimize the decomposition of the starting phosphinidene complex. The structures of compounds 3, 5, 6a, and 6c have been determined through X-ray diffraction methods and are discussed below. The formation of compounds 3 to 6 can be viewed as resulting from the biphilic interaction between the multiple Mo-P bond present in compounds 1 and 2 and the corresponding methylene-like M(CO)n fragments, thus resembling the formation of polynuclear complexes and clusters through the addition of related metal fragments to the multiple M-C bonds of transition-metal carbene and carbyne complexes.20 Surprisingly, however, this synthetic strategy has been rarely explored previously using asymmetric phosphinidene complexes of type E. Actually we can quote only one precedent for this sort of reaction. In particular, the roomtemperature reaction of the phosphinidene-bridged MnFe complex [FeMnCp*(μ-PR)(CO)6] with Fe2(CO)9 has been reported to give the corresponding Fe(CO)4 adduct [Fe2MnCp*(μ3-PR)(CO)10], a molecule closely related to compounds 3 and 5, although not fully characterized at the time.8d Solid-State and Solution Structure of the Iron Derivatives 3 and 5. The molecular structure of 3 was reported in our preliminary communication, and it is shown in Figure 3, while the most relevant bond distances and angles are collected in Table 4. The molecule is derived from the addition of a pseudooctahedral Fe(CO)4 fragment to the short P-Mo bond of compound 1, almost perpendicularly to the Mo2P plane. As a result, however, both Mo-P distances are elongated by almost 0.2 A˚. In particular, the long Mo-P length of 2.5953(7) A˚ is now fully consistent with the formulation of a single bond, while the shorter Mo-P length of 2.4390(7) A˚ has a value closer to those of single-dative PfMo bonds (ca. 2.45 A˚ for MoPR3 complexes) or to those found in PR2-bridged Mo complexes (ca. 2.40 A˚). Actually, the interatomic distances within the MoPFe ring of 3 are very close to those measured for the dimetallic dicyclohexylphosphide complex [MoFe(μ-PCy2)(CO)6]21 (ca. 2.93, 2.41, and 2.28 A˚ for the Mo-Fe, Mo-P, and Fe-P bonds, respectively) and related species.22 Thus, the formulation of single M-P and (20) Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89. (21) Alvarez, C. M.; Alvarez, M. A.; Garcı´ a, M. E.; Ramos, A.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Organometallics 2007, 26, 321. (22) (a) Lindner, E.; St€angle, M.; Hiller, W.; Fawzi, R. Chem. Ber. 1988, 121, 1421. (b) Hsiao, S. M.; Shyu, S. G. Organometallics 1998, 17, 1151.

Article


4389

Table 4. Selected Bond Lengths (A˚) and Angles (deg) for Compounds 3, 5, 6a, and 6c parametera

3b

5

6a

6c

Mo1-P Mo2-P M-P Mo1-M H/C-P Mo2-P-Mo1 H/C-P-Mo1 H/C-P-Mo2 H/C-P-M Mo1-P-M Mo2-P-M P-M-Mo1 P-Mo1-M

2.4390(7) 2.5953(7) 2.2969(8) 2.9328(5) 1.789(3) 152.33(3) 123.6(1) 56.4(1) 112.3(1) 76.46(3) 130.84(3) 53.95(2) 49.59(2)

2.4688(6) 2.5990(6) 2.3458(7) 2.9216(4) 1.31(2) 138.96(2) 104(1) 102(1) 103(1) 74.67(2) 129.45(2) 54.58(2) 50.75(2)

2.447(1) 2.613(1) 2.510(1) 3.082(1) 1.33(3) 135.01(4) 104(1) 105(1) 99(1) 76.88(4) 130.39(4) 50.64(3) 52.48(3)

2.446(1) 2.607(2) 2.628(1) 3.162(1) 1.22(5) 134.3(1) 104(2) 109(2) 96(2) 77.00(4) 129.08(6) 48.91(3) 54.09(3)

Bond lengths and angles in A˚ or deg, respectively, according to the labeling shown in the figure. a

b

Figure 4. ORTEP diagram (30% probability) of compound 5, with H atoms (except the one bound to P) and tBu groups omitted for clarity.

Data taken from ref 12.

single-dative MofP bonds for this molecule (Scheme 1), as required by application of the EAN formalism, is fully consistent with the structural data. The most unusual structural feature in 3, however, is the chemical environment around the P atom, which is not of the common tetrahedral type, but rather is of a distorted trigonal-pyramidal type, since the P and metal atoms are almost in the same plane (sum of M-P-M angles 359.6°), with the vertex of the pyramid being occupied by the C atom of the cyclopentadienylidene group. Incidentally, this carbon atom (also in an unusual environment) keeps a strong binding to both the Mo and P atoms, as judged from their short bond lengths of 2.191(3) and 1.789(3) A˚, respectively, which are comparable to the corresponding values of 2.208(5) and 1.807(6) A˚ in the precursor 1.12 In contrast, the geometrical environment around the P atom in the phosphinidene complex 5 is of the common tetrahedral type (Figure 4). Actually this molecule can be viewed as a phosphide-bridged complex of the type [MoFe(μ-PRR0 )(CO)6] in which one of the substituents has been replaced by a 17-electron metallocene fragment MoCpL. Indeed, the interatomic distances within the MoFeP ring of 5 are similar to those in the mentioned phosphide complexes, although the P-M lengths are a bit longer than those in 3 (Table 4). Besides this, we must note that the P-Mo(metallocene) length of 2.5990(6) A˚ is almost identical to that in 3, even when there are no links now (other than this bond) connecting the phosphorus atom with the metallocene fragment that could constrain the length of this bond. The origin of the unusual environment around the P atom in 3 was not obvious, so we carried out DFT calculations on this molecule in search for likely explanations. First, we noticed that the DFT-optimized structure of 3 was in good agreement with the structure determined crystallographically (see the Supporting Information), especially where the planarity of the Mo2PFe skeleton is concerned. This excludes the (remote) possibility that the geometry around phosphorus found in the solid-state structure might be dictated by packing forces. Second, we examined the MOs of the molecule in search for residual π-type bonding interactions that might alternatively justify the planarity of the

Figure 5. ORTEP diagram (30% probability) of compounds 3 (left) and 5 (right), with H atoms (except the one bound to P) omitted for clarity, viewed along the Mo-Fe bond.

Mo2PFe skeleton, but found no signs of them either. Therefore we have to conclude that the unusual geometry around phosphorus in complex 3 is a combination of steric effects and the geometrical restrictions imposed by the bifunctional PC5H4 ligand (connected to one of the Mo atoms through both the phosphorus atom and its C5 ring). This can be better appreciated by examining the projections of the experimental structures of 3 and 5 viewed along the newly formed Fe-Mo bond (Figure 5). Any rotation of the metallocene fragment in 3 so as to reach a conformation comparable to that of 5 (and therefore a more common tetrahedral arrangement around phosphorus) would imply a prohibitive approach of the bulky arene ring to the MoFeCp(CO)6 fragment. In contrast, in the case of 5 the absence of geometrical restrictions, added to the small size of the unidentate PH ligand, allows a tetrahedral arrangement around phosphorus without imposing severe steric repulsions between the metallocene and the carbonylic metal fragment. Spectroscopic data in solution for compounds 3 and 5 are consistent with the solid-state structures just discussed (Table 5 and Experimental Section). In the first place, both complexes exhibit, in addition to the expected two lowfrequency bands arising from the MoCp(CO)2 fragment, four medium to strong C-O stretching bands in the range 2060-1950 cm-1 of the corresponding IR spectra, as expected from the presence of a pseudooctahedral M(CO)4 fragment.23 Moreover, the observation of three different 1H NMR resonances for the cyclopentadienylidene group in 3 (with 1:2:1 relative intensities) and of two different 13C NMR resonances for the Fe(CO)4 fragment in 5 (with 3:1 relative intensities) is indicative of the retention in solution of the asymmetric solidstate conformations and also of the absence of dynamic effects. On the other hand, the change operating in the coordination of (23) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London, U.K., 1975.

4390


Alvarez et al.

Table 5. Selected IR and 31P{1H} NMR Data for New Compounds compounda

ν(CO)b

δP [JHP]c

[Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2L] (1)d [Mo2Cp2(μ-PH)(CO)2L] (2) [FeMo2Cp(μ-κ1:κ1:κ1,η5-PC5H4)(CO)6L] (3) [CrMo2Cp(μ-κ1:κ1:κ1,η5-PC5H4)(CO)7L] (4a) [Mo3Cp(μ-κ1:κ1:κ1,η5-PC5H4)(CO)7L] (4b) [WMo2Cp(μ-κ1:κ1:κ1,η5-PC5H4)(CO)7L] (4c) [FeMo2Cp2(μ3-PH)(CO)6L] (5) [CrMo2Cp2(μ3-PH)(CO)7L] (6a) [Mo3Cp2(μ3-PH)(CO)7L] (6b) [WMo2Cp2(μ3-PH)(CO)7L] (6c) [FeMoCp(μ-PH2)(CO)6] (7) [CrMoCp(μ-PH2)(CO)7] (8a) [Mo2Cp(μ-PH2)(CO)7] (8b) [MoWCp(μ-PH2)(CO)7] (8c)

1929 (vs), 1858 (s) 1908 (vs), 1833 (s) 2056 (s), 2002 (m), 1985 (s), 1976 (s), 1927 (s), 1860 (m) 2047 (m), 1972 (w), 1959 (s, sh), 1957 (vs), 1937 (m), 1908 (w), 1875 (w) 2061 (m), 1986 (w), 1965 (vs), 1960 (s), 1943 (m), 1925 (w), 1870 (w) 2061 (m), 1978 (w), 1960 (vs), 1955 (s), 1939 (m), 1924 (w), 1871 (w) 2045 (s), 1987(w), 1972 (vs), 1966 (vs), 1916 (s), 1845(m) 2039 (m), 1972 (w), 1949 (vs), 1942 (s), 1927 (s), 1909 (w), 1858 (m) 2053 (m), 1971 (m), 1954 (vs), 1947 (s), 1938 (s), 1916 (m), 1853 (m) 2054 (m), 1969 (m), 1949 (vs), 1944 (s), 1933 (s), 1915 (m), 1853 (m). 2076 (s), 2022 (m), 2000 (s, sh), 1996 (vs), 1950 (s), 1888 (s) 2064 (m), 1996 (w), 1986 (m), 1972 (vs), 1955 (s), 1923 (m), 1902 (w) 2077 (m), 2008 (m), 1990 (s), 1960 (vs), 1948 (s), 1940 (m), 1898 (m) 2077 (m), 2001 (m), 1983 (s), 1969 (vs), 1954 (s), 1941 (m), 1898 (m).

501.5 503.3 [183] 206.5 269.7 263.1 228.6 100.3 [220] 181.1 [221] 176.4 [220] 135.5 [227] 2.2 [360] 56.4 [379, 349] 35.8 [379, 349] 14.0 [390, 358]

a L = η6-1,3,5-C6H3tBu3. b Recorded in petroleum ether solution; C-O stretching bands (ν(CO)) in cm-1. c Recorded in C6D6 solutions at 290 K and 121.50 MHz; δ in ppm relative to external 85% aqueous H3PO4. d Data taken from ref 5a.

the phosphinidene ligand upon formation of compounds 3 and 5, from the μ2 to the μ3 mode, is accompanied by a dramatic shielding of the P nucleus (300-400 ppm), much stronger for the phosphinidene complex; thus, the chemical shifts are now ca. 100-200 ppm lower than those typically observed for μ3-PR ligands in metal clusters.24 For instance, the trinuclear cluster [Mo2FeCp2(μ3-PPh)(CO)7] gives rise to a significantly more deshielded resonance (292.4 ppm).25 It is very likely that the strong shielding of the 31P resonances in compounds 3 and 5 (a feature also reproduced in the isoelectronic compounds 4 and 6; see Table 5) is related to the absence of metalmetal bonds connecting the metal atoms in these molecules and the much wider M-P-M angles (compared to those found in triangular clusters) derived from this circumstance (Mo2-P-M angles in the range 130-150°, Table 4). The relevance of these factors, well established for PR2-bridged complexes, has been also recognized previously in the case of several polynuclear phosphinidene-bridged complexes.24 Solid-State Structures of the Phosphinidene-Bridged Complexes 6a and 6c. The structure of the chromium compound 6a is depicted in Figure 6, while that of the tungsten compound 6c is completely analogous (see the Supporting Information), except for the expected lengthening in the bonds involving the group 6 metal atom (Table 4). Actually, the structure of these two molecules is very similar to that of the iron compound 5 discussed above, by just replacing the Fe(CO)4 fragment with a pseudooctahedral M(CO)5 group (M = Cr, W). Except for the distances involving the chromium or tungsten atoms, all other internuclear separations are very similar to those found in 5 (and also to those in 3, Table 4). In particular, the distances of ca. 2.60 and 2.45 A˚ for the Mo2-P and Mo1-P lengths justify their formulation as single and single-dative bonds, respectively, while the values of ca. 2.15 (Cr) and 2.63 A˚ (W) for the P-M separations within the MoMP ring are consistent with their formulation as single bonds, all in agreement with the corresponding localized descriptions according to the EAN formalism. The conformation of the metallocene fragment with respect to the carbonyl moieties in these heptacarbonyl complexes is also the same as that found in the iron compound 5, that is, the one implying an anti arrangement of the (24) Carty, A. J.; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G.; Quin, L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 16. (25) Bridgeman, A. J.; Mays, M. J.; Woods, A. D. Organometallics 2001, 20, 2076.

Figure 6. ORTEP diagram (30% probability) of compound 6a, with H atoms (except the one bound to P) and tBu groups omitted for clarity.

Cp ligands. No doubt this is the conformation minimizing the repulsions between the sterically more demanding groups being present there, particularly the very bulky arene ligand, which in this way is the group bending away as much as possible from the carbonylic metal moieties. A further indication of the steric constraints in this molecule is apparent in the pentacarbonylic fragment of the chromium compound, in which the equatorial carbonyl closer to the MoCp(CO)2 fragment (C(5) 3 3 3 Mo(1) = 2.775(4) A˚) bends away from this fragment (Cr-C-O= 163.3(3)o, Mo-CrC=62.5(1)o). Such a distortion is not present in the tungsten compound, because of the higher covalent radius of tungsten: the closest W-CO approach to the MoCp(CO)2 fragment is already 3.008(7) A˚. As found for the iron compound 3, a DFT calculation on the chromium compound 6a gave an optimized structure in good agreement with the experimental one (see the Supporting Information), this proving that the structural features discussed above are intramolecular in origin and not due to unadvertised packing forces in the crystal. In particular, we note that the calculation correctly predicts a very large Mo2-P separation (2.674 A˚) with a quite low electron density at the corresponding bcp (0.378 e A˚-3, Table 3). All of this suggests that the bond connecting the metallocene fragment to the rest of the molecule in the heterometallic complexes 3 to 6 is quite weak. As we will discuss later, actually this bond is easily cleaved in the absence of further links of the metallocene fragment, as in the case of the PH-bridged compounds. Solution Structure of the Heterometallic Complexes 4 and 6. The spectroscopic data for compounds 4a-c and

Article

6a-c (Table 5 and Experimental Section) are similar within each series and are in turn consistent with the retention in solution of the solid-state structures discussed above. In the first place, the corresponding IR spectra of all these complexes exhibit, in addition to the expected two low-frequency bands arising from the MoCp(CO)2 fragment, four or five medium to strong C-O stretching bands in the range 2060-1930 cm-1, corresponding to the presence of a pseudooctahedral M(CO)5 fragment.23 For compounds 4, the asymmetry introduced by the addition of the M(CO)5 fragment perpendicularly to the plane bisecting the molecule in the starting compound is denoted by the appearance of three to four distinct CH resonances for the PC5H4 ligand in the corresponding 1H and 13C NMR spectra and also by the appearance of two distinct carbonyl resonances for the MoCp(CO)2 fragment, these exhibiting large (ca. 22 Hz) or negligible two-bond coupling to phosphorus, as expected respectively for cis and trans relative positioning of these ligands in a piano-stool fragment.26 The latter spectroscopic feature can be also appreciated in compound 6. On the other hand, the bridgehead carbon atom of the PC5H4 ligand in compounds 4 gives rise to a 13C resonance strongly coupled to phosphorus as expected (JPC = 45 Hz), with a chemical shift (ca. 98 ppm) that can be considered as unremarkable for a substituted cyclopentadienyl ligand. We note, however, that no other data for cyclopentadienylidene-phosphinidene complexes are available for comparative purposes, since the corresponding resonance in the starting complex 1 could not be located in the corresponding 13C NMR spectra.5a The M(CO)5 fragments in all compounds 4 and 6 give rise to particularly weak carbonyl resonances (compared to those of the MoCp(CO)2 fragment) due to poor longitudinal relaxation. Actually, rather than the five resonances expected in the absence of dynamic effects for this fragment, only one sharp resonance was observed in most cases. Fortunately, complex 6c gave somewhat more intense resonances for the W(CO)5 fragment, which turned out to be two doublet resonances (JPC 10 and 5 Hz) with 4:1 intensities, respectively. From this it follows that the W(CO)5 fragment undergoes a fast (on the NMR time scale) rotation around the W-CO(axial) vector in solution at room temperature, thus rendering an average resonance for the four equatorial carbonyls. Having interpreted this, we then conclude that the single resonance observed for all other complexes 4 and 6 corresponds to the average resonance of the four equatorial carbonyls of the corresponding M(CO)5 fragment in each case, while the fifth resonance of these fragments would be lost in the baseline of the corresponding spectra, due to its very weak intensity. The phosphinidene ligands in compounds 4 and 6 give rise to quite shielded 31P NMR resonances, as found for the iron derivatives 3 and 5, these showing the usual shielding effect down the triad (Cr < Mo < W), and for the PH complexes, giving resonances some 100 ppm lower than the corresponding PC5H4 counterparts. It should be noted that all the μ3-PH complexes 5 and 6 exhibit unexpectedly low P-H couplings of ca. 220 Hz, some 40 Hz higher than that in the starting (26) For complexes of type [MoCpXYL2] it is well established that JXY coupling constants increase algebraically with the X-Mo-Y angle, being usually negative at acute angles. See, for instance: (a) Jameson, C. J. In Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G.; Quin, L. D., Eds.; VCH: New York, 1987; Chapter 6. (b) Wrackmeyer, B.; Alt, H. G.; Maisel, H. E. J. Organomet. Chem. 1990, 399, 125. 2


4391

Figure 7. Influence of the geometrical distortions in μ2- and μ3-PH ligands on the corresponding one-bond P-H couplings.

complex 2 (Table 5), but substantially lower than the usual values in the range 260-340 Hz measured for related isoelectronic trinuclear compounds having μ3-PH ligands.4c,e,h An examination of the pertinent spectroscopic data for other polynuclear complexes and clusters having μ3-PH ligands revealed that the corresponding P-H couplings are somewhat higher when the PH ligand bridges three metal atoms linked by two metal-metal bonds (290-340 Hz)4g,27 and even higher when bridging a metal triangle.4a,28 By recalling that the magnitude of the one-bond P-H couplings is largely determined by the Fermi contact term, which in turn is related to the s atomic orbital contribution to the pertinent P-H bond,26a we can interpret these different values as derived from the fine geometrical differences in the phosphorus environment among all these species (Figure 7). For a PH ligand bridging a triangular face, the short M-M distances impose relatively low M-P-M angles, and therefore the M-P-H angles are relatively high (above 130°), hence with a large s orbital contribution from the phosphorus atom. After removal of two metal-metal bonds, the steric repulsions take the unbound metal fragment as far away as possible from the metal-metal bonded fragments, thus opening the corresponding M-P-M angles (and reducing the M-P-H ones). In the limit, this distortion would imply a trigonal-pyramidal environment around phosphorus, with the P-H bond therefore being made up from a pure p orbital from phosphorus and thus providing a minimum contribution to the P-H coupling. As we have discussed above, the M-P-M angles involving the bulky metallocene fragment in compounds 5 and 6 are quite large (130-140°), and accordingly the H-P-M angles are substantially reduced (95-105°), thus confirming a significant distortion toward the TP limit and, hence, explaining the anomalous low P-H couplings. As it seems, the magnitude of the P-H coupling might therefore be used as a diagnostic tool for detecting fine geometrical distortions in polynuclear complexes bridged by PH ligands. At first glance, the above considerations should lead to the prediction that μ2-PH ligands should exhibit larger P-H couplings than μ3-PH ligands since, in an ideal geometry, the P-H bond in the first case should have a greater s orbital contribution from phosphorus (sp2 vs sp3 hybrid orbitals). Indeed this is the trend well established for one-bond C-H couplings in organic molecules. However, an analysis of the geometrical parameters in the computed structure of 2 reveals that, surely because of the great steric demands of (27) Bautista, M. T.; White, P. S.; Schauer, C. K. J. Am. Chem. Soc. 1991, 113, 8963. (28) Sunick, D. L.; White, P. S.; Schauer, C. K. Organometallics 1993, 12, 245.

4392


the metal fragments and the small size of the hydrogen atom, the M-P-M and M-P-H angles deviate largely from the ideal value of 120°, moving toward a T-shaped geometry, in which the P-H bond again would be made up from a pure p orbital from phosphorus, with this therefore leading once more to a reduced P-H coupling. Actually, the computed M-P-H angles for 2 (102.5° and 116.9°) are comparable to those measured in compounds 5 and 6, thus justifying at least in part the anomalously low P-H coupling also observed for the binuclear compound 2. Hydrolysis of the Phosphinidene Complexes 5 and 6. Synthesis of PH2-Bridged Derivatives. During the present research it was observed that the phosphinidene complexes 5 and 6 would progressively decompose during manipulation in a way not paralleled by their PC5H4 counterparts. Independent experiments revealed that this was caused by a quite selective reaction taking place with water. Actually, upon stirring of dichloromethane solutions of compounds 5 and 6a-c with a moderate excess of degassed water at room temperature for 5-8 h, a degradation of these phosphinidene complexes takes place to give with good yields the corresponding binuclear phosphide-bridged complexes [FeMoCp(μ-PH2)(CO)6] (7) and [MMoCp(μ-PH2)(CO)7] (M=Cr (8a), Mo (8b), W (8c)), which could be isolated as pure microcrystalline solids in a conventional way (Scheme 3). The formation of these phosphide complexes requires the cleavage of the metal-phosphorus bond involving the metallocene fragment, which might be eliminated initially perhaps in the form of the hydroxo complex [MoCp(OH)L], although we have not been able to identify the actual metallocene product or products in the crude reaction mixture. Besides this, we note that the P-Mo bond cleavage reaction leading to the phosphide complexes 7 and 8 could be also induced through protonation. Thus, an independent experiment revealed that the trimolybdenum compound 6b reacted rapidly in dichloromethane solution at room temperature with one equivalent of [H(OEt2)2](BAr0 4) (Ar0 = 3,5-C6H3(CF3)2) to give almost quantitatively the phosphide complex 8b. However, we were not able to identify the corresponding metallocene product or products in this reaction. It should be stressed that the cyclopentadienylidenephosphinidene complexes 3 and 4 do not react with water under comparable conditions, even when the Mo-P bond connecting the metallocene fragment with the rest of the molecule seems to be as weak as the corresponding bonds in the phosphinidene compounds 5 and 6, as deduced from the X-ray data and DFT calculations discussed above. It seems therefore that the presence of a second connection between these fragments (the P-C5H4 bond) would be a critical factor stabilizing these heterometallic compounds toward hydrolysis. The structure proposed for compounds 7 and 8 is based on those determined crystallographically for the dicyclohexylphosphide complexes [FeMoCp(μ-PCy2)(CO)6]21 and [Mo2Cp(μ-PCy2)(CO)7]29 and related species. Indeed, the IR spectra of compounds 7 and 8 exhibit C-O stretching bands with a pattern similar to those reported previously for the corresponding dicyclohexylphosphide complexes, but shifted toward higher wavenumbers as expected. The presence of the PH2 ligand in compounds 7 and 8 is readily apparent from the corresponding (29) Alvarez, M. A.; Garcı´ a, M. E.; Martı´ nez, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2009, 28, 6293.

Alvarez et al. Scheme 3

31

P NMR spectra, these showing in each case a resonance in the range 0-50 ppm displaying large one-bond couplings (350390 Hz) with two hydrogen atoms. For the heptacarbonyl compounds 8a-c, the latter hydrogen atoms give rise to separate NMR resonances at ca. 5 ppm, as expected for the proposed structures. The hexacarbonyl complex 7, however, gives rise to a single PH resonance, this revealing the occurrence of a fast dynamic process in solution that creates an apparent mirror plane containing the metal and P atoms. This might be accomplished by rotation of the MoCp(CO)2 fragment, a rearrangement established to occur easily in the dimolybdenum complexes of the type [Mo2Cp2(μ-H)(μ-PRR0 )(CO)4],30,31 which have two MoCp(CO)2 fragments connected by phosphide and hydride ligands. In agreement with this, the 13C NMR spectrum of 7 at room temperature exhibits a single, average resonance at 238.1 ppm for the Mo-bound carbonyls (displaying an also average P-C coupling of 11 Hz). In addition, this spectrum also exhibits a single average resonance at 210.2 ppm for the Fe-bound carbonyls. This indicates that the dynamic process in operation must in turn involve the mutual exchange of the carbonyls at the iron center, although we have not studied this matter in detail. The fact that the heptacarbonyl compounds 8a-c behave instead as rigid molecules might be reasonably explained by taking into account that the higher steric demands of the pentacarbonyl fragments (compared to a Fe(CO)4 one) would make such a rearrangement more difficult.

Concluding Remarks The geometrical constraints imposed by the bifunctional κ1:κ1,η5-PC5H4 bridging ligand, when compared to the simple PH ligand, have significant effects on the structure and reactivity of the corresponding dimolybdenum complexes 1 and 2. Concerning their ground-state structures, the presence of the PC5H4 ligand in 1 imposes a wider Mo-P-Mo angle and causes a significant delocalization of the metalphosphorus π-bonding interaction along the Mo-P-Mo chain. In contrast, this interaction in the PH-bridged complex 2 is essentially localized on the Mo-P bond involving the 15-electron metal fragment and is then best described as a double bond. In spite of this significant difference, both complexes behave similarly when faced with 16-electron metal fragments of the type M(CO)n, to give trinuclear complexes (30) Garcı´ a, M. E.; Riera, V.; Ruiz, M. A.; Saez, D. Organometallics 2002, 21, 5515. (31) (a) Henrick, K.; McPartlin, M.; Horton, A. D.; Mays, M. J. J. Chem. Soc., Dalton Trans. 1988, 1083. (b) Woodward, S.; Curtis, M. D. J. Organomet. Chem. 1992, 439, 319.

Article


derived from the biphilic interaction between these methylenelike fragments and the multiple, carbene-like Mo-P bond. This interaction is quite strong, as judged from the significant increase seen in the Mo-P lengths of the starting materials. Presumably all trinuclear derivatives bridged by the PC5H4 ligand (3 and 4a-c) display an anomalous chemical environment around the P atom, which is of a distorted trigonalpyramidal type, whereas the PH-bridged complexes (5 and 6a-c) display a more conventional (even if distorted) tetrahedral environment around phosphorus. The absence of any significant residual M-P π-bonding interaction in all these complexes, as indicated by DFT calculations, leads us to conclude that the unusual TP geometry around phosphorus in the PC5H4 compounds is a combination of steric effects and the geometrical restrictions derived from the bifunctional coordination of this ligand. Finally, this coordination mode of the PC5H4 ligand stabilizes the corresponding trinuclear derivatives toward hydrolysis, while their PH-bridged analogues undergo easily the hydrolytic cleavage of their P-Mo(metallocene) bonds to give binuclear PH2-bridged derivatives.

Experimental Section General Procedures and Starting Materials. All manipulations and reactions were carried out under a nitrogen (99.995%) atmosphere using standard Schlenk techniques. Solvents were purified according to literature procedures and distilled prior to use.32 Petroleum ether refers to that fraction distilling in the range 338-343 K. Compounds 1 and [Mo2Cp2(μ-P)(CO)2L][BAr0 4] (L = η6-1,3,5-C6H3tBu3) were prepared as described previously.5a,10 Tetrahydrofuran (THF) solutions of the solvates [M(CO)5(THF)] were prepared in situ by literature methods.33 All other reagents were obtained from the usual commercial suppliers and used as received. Chromatographic separations were carried out using jacketed columns cooled by tap water (ca. 288 K) or by a closed 2-propanol circuit, kept at the desired temperature with a cryostat. Low-temperature reactions were performed using jacketed Schlenk tubes, refrigerated analogously. Commercial aluminum oxide (activity I, 150 mesh) was degassed under vacuum prior to use. The latter was mixed under nitrogen with the appropriate amount of water to reach the activity desired. Filtrations were carried out using dry diatomaceous earth. IR C-O stretching frequencies were measured in solution and are referred to as ν (CO). Nuclear magnetic resonance (NMR) spectra were routinely recorded at 300.13 (1H), 121.50 (31P{1H}), or 75.48 MHz (13C{1H}) at 290 K in CD2Cl2 solutions unless otherwise stated. Chemical shifts (δ) are given in ppm, relative to internal tetramethylsilane (1H, 13C) or external 85% aqueous H3PO4 (31P). Coupling constants (J) are given in hertz. Preparation of [Mo2Cp2(μ-PH)(CO)2L] (2). A THF solution (8 mL) of compound [Mo2Cp2(μ-P)(CO)2L][BAr0 4] (0.060 g, 0.040 mmol) was cooled at 195 K. Then Li[BHEt3] (44 μL of a 1 M solution in THF, 0.044 mmol) was added, and the mixture was stirred at that temperature for 1 min to give a red-purple solution. The solvent was then removed under vacuum, the residue was extracted with toluene-petroleum ether (1:2), and the extracts were filtered using a canula. Removal of the solvents under vacuum and washing of the residue with petroleum ether (4 mL) gave a red residue containing reasonably pure compound 2, which could be used for subsequent reactions. Further purification of this crude product could be achieved through chromatography on alumina (activity IV) at 243 K. Elution with (32) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003. (33) Strohmeier, W. Angew. Chem. 1964, 76, 873.

4393

dichloromethane-petroleum ether (1:8) then gave a purple band yielding, after removal of solvents under vacuum, compound 2 as a wine-red, quite air-sensitive microcrystalline solid (0.022 g, 84%). IR ν(CO) (THF): 1890 (vs), 1811 (s). 1H NMR (C6D6): δ 12.47 (d, JHP = 183, 1H, PH), 5.41 (s, 5H, Cp), 4.80 (d, JHP = 4, 5H, Cp), 4.70 (d, JHP = 4, 3H, C6H3), 1.05 (s, 27H, t Bu). 13C{1H} NMR (233 K, tol-d8): δ 247.8 (s, br, MoCO), 103.6 [s, C(C6H3)], 91.2, 85.3 (2s, Cp), 78.6 [s, CH(C6H3)], 33.2 [s, C1(tBu)], 30.2 [s, C2(tBu)]. Preparation of [FeMo2Cp(μ-K1:K1:K1,η5-PC5H4)(CO)6L] (3). Solid [Fe2(CO)9] (0.025 g, 0.069 mmol) was added to a tetrahydrofuran solution (5 mL) of compound 1 (0.027 g, 0.041 mmol) at 223 K, and the mixture was stirred while allowing the temperature to reach 273 K. After 6 h stirring at that temperature the solvent and all volatile substances were removed under vacuum, the residue was extracted with petroleum ether (5 5 mL), and the extracts were chromatographed on an alumina column (activity IV) at 263 K. Elution with dichloromethanepetroleum ether (1:4) gave a yellow-green fraction, yielding, after removal of solvents under vacuum, compound 3 as a brown-yellow microcrystalline solid (0.028 g, 82%). The crystals used in the X-ray study of 3 were grown by slow diffusion at 253 K of a layer of petroleum ether into a concentrated solution of the complex in toluene. Anal. Calcd for C34H39FeMo2O6P: C, 49.66; H, 4.78. Found: C, 49.53; H, 4.70. 1H NMR (C6D6): δ 5.02 (s, 5H, Cp), 4.87 (d, JHP = 4, 3H, C6H3), 4.81 (m, 1H, C5H4), 4.48 (m, 2H, C5H4), 4.38 (m, 1H, C5H4), 1.08 (s, 27H, t Bu). Preparation of [CrMo2Cp(μ-K1:K1:K1,η5-PC5H4)(CO)7L] (4a). A freshly prepared tetrahydrofuran solution (5 mL) of [Cr(CO)5(THF)] (prepared from 0.015 g of [Cr(CO)6], ca. 0.068 mmol) was added to a dichloromethane solution (3 mL) of compound 1, prepared in situ (ca. 0.023 g, 0.035 mmol), and the mixture was stirred at room temperature for 1 min to give a dark rose solution. After removal of solvents under vacuum, the residue was extracted with dichloromethane-petroleum ether (1:5) and the extracts were chromatographed on an alumina column (activity IV) at 288 K. Elution with the same solvent mixture gave a red-purple fraction, yielding, after removal of solvents under vacuum, compound 4a as a rose-red, quite air-sensitive microcrystalline solid (0.018 g, 61%). 1H NMR (400.13 MHz, C6D6): δ 5.03 (s, br, 3H, C6H3), 5.00 (m, 1H, C5H4), 4.96 (s, 5H, Cp), 4.76, 4.60, 4.10 (3 m, 3 1H, C5H4), 1.10 (s, 27H, tBu). 13C{1H} NMR: δ 243.5 [d, JCP = 23, MoCO], 236.3 [s, MoCO], 225.6 [d, JCP = 2, 4CrCO], 112.8 [s, br, C(C6H3)], 97.5 [d, JCP=45, C1(C5H4)], 93.0 (s, Cp), 91.5 [d, JCP=4, CH(C5H4)], 87.7 [d, JCP = 5, CH(C5H4)], 86.0 [s, CH(C5H4)], 85.4 [d, JCP = 5, CH(C5H4)], 72.1 [s, CH(C6H3)], 35.3 [s, C1(tBu)], 31.4 [s, C2(tBu)]. Preparation of [Mo3Cp(μ-K1:K1:K1,η5-PC5H4)(CO)7L] (4b). The procedure is analogous to that described for compound 4a, but using [Mo(CO)5(THF)] (prepared from 0.030 g of [Mo(CO)6], ca. 0.114 mmol). After similar workup, a purple fraction was collected using dichloromethane-petroleum ether (1:7), yielding, after removal of solvents under vacuum, compound 4b as a purple microcrystalline solid (0.022 g, 70%). Anal. Calcd for C35H39Mo3O7P: C, 47.21; H, 4.41. Found: C, 46.91; H, 4.20. 1H NMR (C6D6): δ 5.20-4.90 (m, 4H, C6H3 and C5H4), 4.95 (s, 5H, Cp), 4.60 (m, 2H, C5H4), 4.07 (m, 1H, C5H4), 1.10 (s, 27H, tBu). 13C{1H} NMR: δ 242.2 [d, JCP = 22, MoCO], 236.5 [s, MoCO], 211.4 [d, JCP = 13, 4MoCO], 119.8 [s, C(C6H3)], 98.1 [d, JCP =44, C1(C5H4)], 92.1 (s, Cp), 91.8, 87.8 [2d, JCP =4, CH(C5H4)], 86.8 [s, CH(C5H4)], 85.4 [d, JCP =6, CH(C5H4)], 72.2 [s, br, CH(C6H3)], 35.5 [s, C1(tBu)], 31.5 [s, C2(tBu)]. Preparation of [Mo2WCp(μ-K1:K1:K1,η5-PC5H4)(CO)7L] (4c). The procedure is analogous to that described for compound 4a, but using [W(CO)5(THF)] (prepared from 0.030 g of [W(CO)6], ca. 0.085 mmol). After similar workup, a purple fraction was collected using dichloromethane-petroleum ether (1:5), yielding, after removal of solvents under vacuum, compound 4c as a purple

4394


microcrystalline solid (0.023 g, 67%). Anal. Calcd for C35H39Mo2O7PW: C, 42.97; H, 4.02. Found: C, 42.63; H, 3.98. 1H NMR (C6D6): δ 5.15-4.95 (m, 4H, C6H3 and C5H4), 4.95 (s, 5H, Cp), 4.65, 4.59, 4.09 (3 m, 3 1H, C5H4), 1.10 (s, 27H, tBu). Preparation of [FeMo2Cp2(μ-PH)(CO)6L] (5). Solid [Fe2(CO)9] (0.020 g, 0.060 mmol) was added to a solution (4 mL) of compound 2 (ca. 0.026 g, 0.040 mmol) in toluene-THF (1:1) at 253 K, and the mixture was stirred and allowed to reach room temperature for 30 min. The solvent was then removed under vacuum, the residue was extracted with dichloromethanepetroleum ether (1:2), and the extracts were chromatographed on alumina (activity IV) at 288 K. Elution with the same solvent mixture gave an orange-brown band, yielding, after removal of solvents under vacuum, compound 5 as a brown microcrystalline solid (0.024 g, 75%). The crystals used in the X-ray study of 5 were grown by slow diffusion at 253 K of a layer of petroleum ether into a concentrated solution of the complex in toluene. Anal. Calcd for C34H41FeMo2O6P: C, 49.54; H, 5.01. Found: C, 49.36; H, 5.02. 1H NMR (400.13 MHz, C6D6): δ 5.56 (d, JHP = 220, 1H, PH), 5.10 (s, 5H, Cp), 4.88 (d, JHP = 6, 3H, C6H3), 4.54 (d, JHP = 5, 5H, Cp), 1.31 (s, 27H, tBu). 13C{1H} NMR (100.61 MHz): δ 243.8 [d, JCP = 18, CO], 238.8 [s, CO], 215.5 [m, br, 3FeCO], 210.3 [d, JCP = 10, FeCO], 103.8 [s, C(C6H3)], 91.4, 85.9 [2s, Cp], 79.0 [s, CH(C6H3)], 35.3 [s, C1(tBu)], 31.7 [s, C2(tBu)]. Preparation of [CrMo2Cp2(μ3-PH)(CO)7L] (6a). A freshly prepared tetrahydrofuran solution (2 mL) of [Cr(CO)5(THF)] (prepared from 0.018 g of [Cr(CO)6], ca. 0.080 mmol) was added to a toluene solution (4 mL) of compound 2 (ca. 0.026 g, 0.040 mmol) at 253 K, and the mixture was stirred and allowed to reach room temperature for 10 min. The solvent was then removed under vacuum, the residue was extracted with dichloromethane-petroleum ether (1:3), and the extracts were chromatographed on alumina (activity IV) at 288 K. Elution with the same solvent mixture gave a purple band, yielding, after removal of solvents under vacuum compound 6a as a wine-red microcrystalline solid (0.030 g, 88%). The crystals used in the X-ray study of 6a were grown by slow diffusion at 253 K of layers of toluene and petroleum ether into a concentrated solution of the complex in dichloromethane. Anal. Calcd for C35H41CrMo2O7P: C, 49.54; H, 4.87. Found: C, 49.36; H, 4.79. 1 H NMR (C6D6): δ 7.10 (d, JHP = 221, 1H, PH), 4.94 (s, 5H, Cp), 4.58 (d, JHP = 6, 3H, C6H3), 4.47 (d, JHP = 5, 5H, Cp), 1.11 (s, 27H, tBu). 13C{1H} NMR (100.61 MHz, C6D6): δ 245.9 [d, JCP = 17, MoCO], 237.0 [s, MoCO], 227.5 [s, 4CrCO], 108.2 [s, C(C6H3)], 93.1, 86.4 [2s, Cp], 74.2 [s, CH(C6H3)], 35.4 [s, C1(tBu)], 31.3 [s, C2(tBu)]. Preparation of [Mo3Cp2(μ3-PH)(CO)7L] (6b). The procedure is analogous to that described for compound 6a, but using [Mo(CO)5(THF)] (prepared from 0.022 g of [Mo(CO)6], ca. 0.080 mmol). After similar workup, compound 6b was isolated as a purple microcrystalline solid (0.030 g, 83%). Anal. Calcd for C35H41Mo3O7P: C, 47.10; H, 4.63. Found: C, 47.00; H, 4.54. 1 H NMR (400.13 MHz, C6D6): δ 7.36 (d, JHP = 220, 1H, PH), 4.94 (s, 5H, Cp), 4.58 (d, JHP = 6, 3H, C6H3), 4.45 (d, JHP = 5, 5H, Cp), 1.11 (s, 27H, tBu). Preparation of [Mo2WCp2(μ3-PH)(CO)7L] (6c). The procedure is analogous to that described for compound 6a, but using [W(CO)5(THF)] (prepared from 0.028 g of [W(CO)6], ca. 0.080 mmol). After similar workup, compound 6c was isolated as a purple microcrystalline solid (0.036 g, 90%). The crystals used in the X-ray study of 6c were grown by slow diffusion at 253 K of a layer of petroleum ether into a concentrated solution of the complex in toluene. Anal. Calcd for C35H41Mo2O7PW: C, 42.88; H, 4.22. Found: C, 42.80; H, 4.15. 1H NMR (C6D6): δ 7.02 (d, JHP = 227, 1H, PH), 4.94 (s, 5H, Cp), 4.58 (d, JHP = 6, 3H, C6H3), 4.45 (d, JHP=5, 5H, Cp), 1.10 (s, 27H, tBu). 13C{1H} NMR (100.61 MHz, C6D6): δ 244.2 [d, JCP=17, MoCO], 236.9 [s, MoCO], 201.9 [d, JCP=10, 4WCO], 196.7 [d, JCP = 5, WCO],

Alvarez et al. 107.6 [s, C(C6H3)], 92.5, 86.8 [2s, Cp], 74.6 [s, CH(C6H3)], 35.4 [s, C1(tBu)], 31.4 [s, C2(tBu)]. Preparation of [FeMoCp(μ-PH2)(CO)6] (7). Degassed water (50 μL, 2.78 mmol) was added to a dichloromethane solution (5 mL) of compound 5 (0.016 g, 0.020 mmol), and the mixture was stirred at room temperature for 5 h to give a brown-orange solution. After removal of the solvent under vacuum, the residue was extracted with petroleum ether and the extracts were filtered. Removal of the solvent from the filtrate yielded compound 7 as a brown powder (0.008 g, 96%). Anal. Calcd for C11H7FeMoO6P: C, 31.61; H, 1.69. Found: C, 31.53; H, 1.71. 1H NMR (C6D6): δ 4.56 (s, 5H, Cp), 3.98 (d, JHP=360, 2H, μ-PH2). 13 C{1H} NMR (C6D6): δ 238.1 [d, JCP=11, 2MoCO], 210.3 [d, JCP = 10, 4FeCO], 90.8 (s, Cp). Preparation of [CrMoCp(μ-PH2)(CO)7] (8a). Degassed water (50 μL, 2.78 mmol) was added to a dichloromethane solution (5 mL) of compound 6a (0.017 g, 0.020 mmol), and the mixture was stirred at room temperature for 8 h to give a brown-orange solution. After removal of the solvent under vacuum, the residue was extracted with petroleum ether and the extracts were filtered. Removal of the solvent from the filtrate yielded compound 8a as a brown powder (0.008 g, 90%). Anal. Calcd for C12H7CrMoO7P: C, 32.60; H, 1.60. Found: C, 32.50; H, 1.53. 1H NMR (C6D6): δ 5.12 (dd, JHP = 349, JHH =7, 1H, μ-PH2), 4.85 (dd, JHP =379, JHH =7, 1H, μ-PH2), 4.53 (s, 5H, Cp). Preparation of [Mo2Cp(μ-PH2)(CO)7] (8b). The procedure is similar to that described for 8a, but using compound 6b (0.018 g, 0.020 mmol). This gave compound 8b as a brown powder (0.009 g, 93%). Anal. Calcd for C12H7Mo2O7P: C, 29.65; H, 1.45. Found: C, 29.47; H, 1.41. 1H NMR (C6D6): δ 5.32 (dd, JHP = 349, JHH = 7, 1H, μ-PH2), 4.97 (dd, JHP = 379, JHH = 7, 1H, μ-PH2), 4.57 (s, 5H, Cp). Preparation of [MoWCp(μ-PH2)(CO)7] (8c). The procedure is similar to that described for 8a, but using compound 6c (0.020 g, 0.020 mmol). This gave compound 8c as a brown powder (0.011 g, 95%). Anal. Calcd for C12H7MoO7PW: C, 25.11; H, 1.23. Found: C, 24.99; H, 1.17. 1H NMR (C6D6): δ 5.36 (dd, JHP = 358, JHH = 8, 1H, μ-PH2), 4.97 (dd, JHP = 390, JHH = 7, 1H, μ-PH2), 4.57 (s, 5H, Cp). Computational Details. All computations described in this work were carried out using the GAUSSIAN03 package,34 in which the hybrid method B3LYP was applied with the Becke three-parameter exchange functional35 and the Lee-YangParr correlation functional.36 Effective core potentials and their associated double-ζ LANL2DZ basis set were used for the metal atoms.37 The light elements (P, O, C, and H) were described with the 6-31G* basis.38 Geometry optimizations were performed (34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B.02; Gaussian, Inc.: Wallingford, CT, 2004. (35) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (36) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (37) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (38) (a) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213. (b) Petersson, G. A.; Al-Laham, M. A. J. Chem. Phys. 1991, 94, 6081. (c) Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham, M. A.; Shirley, W. A.; Mantzaris, J. J. Chem. Phys. 1988, 89, 2193.

Article


4395

Table 6. Crystal Data for Compounds 5, 6a and 6c

mol formula mol wt cryst syst space group radiation (λ, A˚) a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z calcd density, g cm-3 absorpt coeff, mm-1 temperature, K θ range, deg index ranges (h, k, l) reflns collected indep reflns (Rint) reflns with I > 2σ(I) R indexesa [data with I > 2σ(I)]

5

6a

6c

C34H41FeMo2O6P 824.37 triclinic P1 0.71073 10.5640(4) 12.8368(5) 14.7378(6) 98.973(2) 98.225(2) 108.721(2) 1829.39(12) 2 1.497 1.149 100 1.43 to 26.39 -13, 12; -16, 15; 0, 18 27 518 7442 (0.0331) 6322 R1 = 0.0259

C35H41CrMo2O7P 848.53 monoclinic P21/c 0.71073 17.782(4) 8.8284(18) 24.281(6) 90 114.275(3) 90 3474.8(13) 4 1.622 1.11 100 1.26 to 26.47 -22, 20; 0, 11; 0, 30 29 935 7167 (0.0685) 5406 R1 = 0.0375

C35H41Mo2O7PW 980.38 monoclinic P21/c 0.71073 17.1750(6) 9.0235(4) 24.1271(9) 90 110.3930(10) 90 3504.8(2) 4 1.858 4.07 100 1.8 to 26.42 -21, 20; 0,11; 0, 30 28 891 7197 (0.0673) 5512 R1 = 0.0331

)

)

wR2 = 0.0689c wR2 = 0.0864d wR2 = 0.0538b R1 = 0.0344 R indexesa R1 = 0.061 R1 = 0.0331 (all data) wR2 = 0.0767c wR2 = 0.0864d wR2 = 0.056b GOF 1.044 1.023 1.019 restraints/params 0/410 0/428 0/428 0.389, -0.518 0.569, -0.76 3.46, -1.038 ΔF(max.,min.), e A˚-3 P P P P a R= Fo| - |Fc / |Fo|. wR = [ w(|Fo|2 - |Fc|2)2/ w|Fo|2]1/2. w = 1/[σ2(Fo2) þ (aP)2 þ bP] where P = (Fo2 þ 2Fc2)/3. b a = 0.0209, b = 1.1031. c a = 0.0124, b = 7.3527. d a = 0.0174, b = 12.6044.

under no symmetry restrictions, using initial coordinates derived from X-ray data of the same or comparable complexes, and frequency analyses were performed to ensure that a minimum structure with no imaginary frequencies was achieved in each case. For interpretation purposes, Mulliken charges were computed as usual,39 and natural population analysis (NPA) charges were derived from the natural bond order analysis of the data.40 Molecular orbitals and vibrational modes were visualized using the Molekel program.41 The topological analysis of F was carried out with the Xaim routine.42 X-ray Structure Determination of Compounds 5, 6a, and 6c. The X-ray intensity data were collected on a Kappa-Appex-II Bruker diffractometer using graphite-monochromated Mo KR radiation at 100 K. The software APEX43 was used for collecting frames with the omega/phi scan measurement method. Bruker SAINT software was used for the data reduction,44 and a multiscan absorption correction was applied with SADABS.45 Using the program suite WinGX,46 the structure was solved by Patterson interpretation and phase expansion and refined with full-matrix least-squares on F2 using SHELXL97.47 In the case of 6c, the structure was solved by direct methods (39) Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833. (40) (a) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735. (b) Reed, A. E.; Curtis, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899. (41) Portmann, S.; L€ uthi, H. P. MOLEKEL: An Interactive Molecular Graphics Tool. CHIMIA 2000, 54, 766. (42) Ortiz, J. C.; Bo, C. Xaim; Departamento de Química Física e Inorganica, Universidad Rovira i Virgili: Tarragona, Spain, 1998. (43) APEX 2, version 2.0-1; Bruker AXS Inc.: Madison, WI, 2005. (44) SMART & SAINT Software Reference Manuals, Version 5.051 (Windows NT Version); Bruker Analytical X-ray Instruments: Madison, WI, 1998. (45) Sheldrick, G. M. SADABS, Program for Empirical Absorption Correction; University of G€ottingen: G€ottingen, Germany, 1996. (46) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (47) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.

using the Sir92 program.48 All the positional parameters and the temperature factors of all the non-H atoms were refined anisotropically, and all hydrogen atoms were geometrically placed and refined using a riding model, except for the P-H atom in each case, which was located in the Fourier maps and refined isotropically. During the refinement of 5, a possible disordered molecule of hexane was found to be present in the asymmetric unit. Therefore, the SQUEEZE procedure,49 as implemented in PLATON,50 was used. Upon SQUEEZE application and convergence, the strongest residual peak (0.39 e A-3) was located around the atom Mo(1). Further details of the data collection and refinements for these compounds are given in Table 6.

Acknowledgment. We thank the DGI of Spain (Projects CTQ2006-01207 and CTQ2009-09444) and the COST Action CM0802 ‘‘PhoSciNet’’ for supporting this work, and the Universidad de Oviedo and the Consejerı´ a de Educaci on of Asturias for grants (to I.A. and J.S.). We also thank the Universidad de Santiago de Compostela (Spain) for the acquisition of the X-ray diffraction data. Supporting Information Available: Tables of atomic coordinates, atomic charges, selected bond distances and angles, selected molecular orbitals and data from the AIM topological analysis for complexes 2, 3, and 6a in pdf format, and a CIF file containing the crystallographic data for the structural analysis of compounds 3, 5, 6a, and 6c. This material is available free of charge via the Internet at http://pubs.acs.org. (48) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435. (49) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194. (50) (a) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, C34. (b) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 1998.

Structure, Bonding, and Reactivity of Binuclear Complexes Having

Recommend Documents