A Bridging Selenoacyl Complex via Alkynylselenolatoalkylidyne

of Advanced Studies, The Australian National University, Canberra, ACT 0200, ... data is made available by participants in Crossref's Cited-by Lin...
0 downloads 0 Views 941KB Size
Download PDF
1526

Organometallics 2010, 29, 1526–1529 DOI: 10.1021/om901079n

A Bridging Selenoacyl Complex via Alkynylselenolatoalkylidyne Rearrangement Lorraine M. Caldwell,† Richard L. Cordiner,† Anthony F. Hill,*,† and J€ org Wagler†,‡ †

Research School of Chemistry, Institute of Advanced Studies, The Australian National University, Canberra, ACT 0200, Australia, and ‡Institut f€ ur Anorganische Chemie, Technische Universit€ at Bergakademie Freiberg, D-09596 Freiberg, Germany Received December 16, 2009 Chart 1. Potential Chalcoacyl Coordination Modesa

Summary: The alkynylselenolatoalkylidyne complex [Mo(t C-Se-CtCSiMe3)(CO)2{HB(pzMe2)3}] (pz=pyrazol-1-yl ) reacts with [RhCl(PPh3)3] via an unusual C-Se bond cleavage/formation sequence to provide the heterodinuclear bridging selenoacyl complex [MoRh( μ^-SeCCtCSiMe3)Cl(CO)2(PPh3){HB(pzMe2)3}], the crystal structure of which reveals a RhMoCSe tetrahedrane core. Although acyl ligands are of central importance to much organotransition metal chemistry, the analogous chalcoacyl ligands (Chart 1) based on the heavier chalcogens, especially selenium and tellurium, remain scarce. With a variety of routes being available for the installation of thiocarbonyl ligands1 there has been some progress in the chemistry of thioacyls derived primarily from migratory insertion processes.2-4 Routes to selenocarbonyl and tellurocarbonyl complexes, however, remain scarce, and accordingly selenoacyls and telluroacyls (Chart 2) are few in *Corresponding author. E-mail: [email protected]. (1) For reviews of the coordination chemistry of carbon monochalcogenides see: (a) Broadhurst, P. V. Polyhedron 1985, 4, 1801. (b) Petz, W. Coord. Chem. Rev. 2008, 252, 1689. (2) (a) Clark, G. R.; Collins, T. J.; Marsden, K.; Roper, W. R. J. Organomet. Chem. 1983, 259, 215. (b) Clark, G. R.; Collins, T. J.; Marsden, K.; Roper, W. R. J. Organomet. Chem. 1978, 157, C23. (c) Rickard, C. E. F.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. J. Organomet. Chem. 2001, 623, 109. (d) Rickard, C. E. F.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. J. Organomet. Chem. 2000, 607, 27. (e) Collins, T. J.; Roper, W. R. J. Organomet. Chem. 1978, 159, 73. (f) Collins, T. J.; Roper, W. R. J. Organomet. Chem. 1977, 139, C9. (g) Elliott, G. P.; Roper, W. R. J. Organomet. Chem. 1983, 250, C5. (h) Elliott, G. P.; Roper, W. R.; Waters, J. M. Chem. Commun. 1982, 811. (i) Clark, G. R.; Johns, P. M.; Roper, W. R.; Wright, L. J. Organometallics 2008, 27, 451. (j) Clark, G. R.; Lu, G.-L.; Roper, W. R.; Wright, L. J. Organometallics 2007, 26, 2167. (k) Clark, G. R.; Marsden, K.; Roper, W. R.; Wright, L. J. J. Am. Chem. Soc. 1980, 102, 6570. (3) (a) Cannadine, J.; Hill, A. F.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 1996, 15, 5409. (b) Hill, A. F.; Schultz, M.; Willis, A. C. Organometallics 2005, 24, 2027. (c) Cowley, A. R. C.; Hill, A. F.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2007, 26, 6114. (d) Bedford, R. B.; Hill, A. F.; White, A. J. P.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1996, 35, 95. (e) Anderson, S.; Cook, D. J.; Hill, A. F.; Malget, J. M.; White, A. J. P.; Williams, D. J. Organometallics 2004, 23, 2552. (f) Cook, D. J.; Hill, A. F. Chem. Commun. 1997, 955. (g) Cook, D. J.; Hill, A. F. Organometallics 2003, 22, 3502. (h) Anderson, S.; Cook, D. J.; Hill, A. F. Organometallics 2001, 20, 2468. (i) Hill, A. F.; Wilton-Ely, J. D. E. T. J. Chem. Soc., Dalton Trans. 1998, 3501. (j) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2007, 26, 3891. (k) Hill, A. F.; Malget, J. M. J. Chem. Soc., Dalton Trans. 1997, 2003. (l) Green, J. C.; Hector, A. L.; Hill, A. F.; Lin, S.; Wilton-Ely, J. D. E. T. Organometallics 2008, 27, 5548. (4) (a) Andon, W.; Ohtaki, T.; Suzuki, T.; Kabe, Y. J. Am. Chem. Soc. 1991, 113, 7782. (b) Drews, R.; Edelmann, F.; Behrens, U. J. Organomet. Chem. 1986, 315, 369. (c) Faraone, F.; Tresoldi, G.; Loprete, G. A. J. Chem. Soc., Dalton Trans. 1979, 933. (d) Tresoldi, G.; Faraone, F.; Piraino, P. J. Chem. Soc., Dalton Trans. 1979, 1053. (e) Ellis, D. D.; Farmer, J. M.; Malget, J. M.; Mullica, D. F.; Stone, F. G. A. Organometallics 1998, 17, 5540. pubs.acs.org/Organometallics

Published on Web 03/10/2010

a

A = O, S, Se, Te.

number, being limited to the mononuclear complexes [Os(η2ACC6H4Me-4)Cl(CO)(PPh3)2] (A = Se, Te)2j and [Mo(η2SeCR)(CO)(L){HB(pz)3}] (pz=pyrazol-1-yl; R=2-thienyl, L=CO, CNC6H2Me3-2,4,6)5 and binuclear complexes of the form [MFe( μ^-ACR)(CO)3(L)2(η-C5H5)] (M=Mo, W; A= Se, Te; L2=(CO)2, μ-dppm; R=C6H4Me-4, C6H3Me2-2,6)6 or [MRu( μ-σ0 -SeCC6H4Me-4)(CO)4(η5-C2B9H11){HB(pz)3}].4e These each have in common that they arise from the addition of chalcogens to mono- or dinuclear alkylidyne complexes. To these may be added the chalcocarbamoyl complexes [Ru(η2-ACNMe2)Cl(CO)(PPh3)2] (A = S, Se, Te), which result from the reactions of the chloroaminocarbene complex [RuCl2(dCClNMe2)(CO)(PPh3)2] with NaAH7 or from (5) Caldwell, L. M.; Hill, A. F.; Willis, A. C. Chem. Commun. 2005, 2615. (6) (a) Gill, D. S.; Green, M.; Marsden, K.; Moore, K.; Orpen, A. G.; Stone, F. G. A.; Williams, I. D.; Woodward, P. J. Chem. Soc., Dalton Trans. 1984, 1343. (b) Anderson, S.; Hill, A. F.; Nasir, B. A. Organometallics 1995, 14, 2987. (c) Byrne, P. G.; Garcia, M. E.; Jeffery, J. C.; Sherwood, P.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1987, 1215. (d) Hill, A. F.; Nasir, B. A.; Stone, F. G. A. Polyhedron 1989, 8, 179. (e) Delgado, E.; Hein, J.; Jeffery, J. C.; Ratermann, A. L.; Stone, F. G. A.; Farrugia, L. J. J. Chem. Soc., Dalton Trans. 1987, 1191. (f) Bermudez, M. D.; Delgado, E.; Elliott, G. P.; Tran-Huy, N. H.; Mayor-Real, F.; Stone, F. G. A.; Winter, M. J. J. Chem. Soc., Dalton Trans. 1987, 1235. (g) Hulkes, A. J.; Hill, A. F.; Nasir, B. A.; White, A. J. P.; Williams, D. J. Organometallics 2004, 23, 679. (7) Wright, A. H.; Roper, W. R. J. Organomet. Chem. 1982, 233, C59. (8) (a) Hill, A. F.; Tocher, D. A.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2005, 24, 5342. (b) Hill, A. F.; Tocher, D. A.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2006, 25, 2108. r 2010 American Chemical Society

Communication

Organometallics, Vol. 29, No. 7, 2010 Scheme 1. Reaction of 1b with 3a

Chart 2. Previously Reported Seleno- and Telluroacyl Complexesa

a

1527

Cp = η-C5H5, pz = pyrazol-1-yl.

oxidative addition of N,N-dimethylthiocarbamoyl chloride to [Ru(CO)2(PPh3)3].8 Although such species, along with dichalcocarboalkoxy complexes LnM-C(dA)AR, fall beyond the scope of this paper, it should be noted that as with hydrocarbyl-substituted chalcoacyls, the prevalence of examples decreases rapidly down group 16. Other than for the telluroacyl complexes [WFe( μ^-TeCC6H4Me-4)(CO)5(η-C5H5)] and [WFe( μ^-TeCC6H4Me-4)(CO)3( μ-dppm)(η-C5H5)],6g no other structural data are currently available for polynuclear seleno- or telluroacyl complexes. The alkynylselenolatoalkylidyne complexes [Mo(tCSe-CtCR)(CO)2{HB(pzMe2)3}] (R=CMe3 1a, SiMe3 1b, C6H4Me-4 1c)9 result from the reactions of halocarbyne complexes [Mo(tCX)(CO)2{HB(pzMe2)3}] (X = Cl, Br)10 with lithium alkynylselenolates (LiSeCtCR). The MotCSe-CtCR spine presents a number of potential sites for interaction with metal reagents. Thus, the reaction of 1a with [Co2(CO)8] results in the conventional addition of the dicobalt unit across the CtC triple bond.9a Subsequent treatment with 1,1-bis(diphenylphosphino)methane (dppm) provides the expected adduct [Mo(tCSe{C2Co2(CO)4( μ-dppm)}tBu)(CO)2{HB(pzMe2)3}]; however it is accompanied by the formation of a small amount of the side product [Mo(tC{C2Co2(CO)4( μ-dppm)}tBu)(CO)2{HB(pzMe2)3}]9c arising from selenium extrusion. In contrast, the reaction of 1a with [Pt(η-C2H4)(PPh3)2] results in initial coordination of the CtC bond to platinum followed by insertion of platinum into the alkynyl C-Se bond to provide isoselenocarbonyl complexes.9b These results coupled with the reaction of alkynyl selenoethers with [RuCl2(PPh3)3] to provide selenolatovinylidene complexes11 indicate that activation of the alkynyl-selenoether linkage by transition metal centers can be quite facile and occurs under comparatively mild conditions. Herein we report the unexpected formation and structural characterization of an unusual heterodinuclear selenoacyl complex, [MoRh( μ^-SeCCtCSiMe3)Cl(CO)2(9) (a) Caldwell, L. M.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organometallics 2008, 27, 341. (b) Caldwell, L. M.; Hill, A. F.; Wagler, J.; Willis, A. C. Dalton Trans. 2008, 3538. (c) Hart, I. J.; Hill, A. F.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1989, 2261. (10) (a) Lalor, F. J.; Desmond, T. J.; Cotter, G. M.; Shanahan, C. A.; Ferguson, G.; Parvez, M.; Ruhl, B. J. Chem. Soc., Dalton Trans. 1995, 1709. (b) Cordiner, R. L.; Hill, A. F.; Wagler, J. Organometallics 2008, 27, 5177. (c) For a review of carbyne chemistry supported by poly(pyrazolyl)borate co-ligands see: Caldwell, L. M. Adv. Organomet. Chem. 2008, 56, 1. (11) Hill, A. F.; Hulkes, A. G.; White, A. J. P.; Williams, D. J. Organometallics 2000, 19, 371.

a

25 C, CH2Cl2, [Mo] = Mo(CO)2{HB(pzMe2)3.

(PPh3){HB(pzMe2)3}] (2), that arises from the reaction of 1b with Wilkinson’s catalyst, [RhCl(PPh3)3] (3).12 Wilkinson’s catalyst (3) forms adducts with simple internal alkynes13 when other subsequent reaction steps are precluded (e.g., dimerization14). The reaction of 3 with the alkynyl thioether 4,7,10-trithiatrideca-2,11-diyne, however, proceeds via a C-S bond cleavage/re-formation sequence to ultimately provide the complex [Rh(CtCMe)Cl(PPh3){κ3-S(CHdCH2)CH2CH2SCHdCMeS}].15 Similarly, we now find that the major product of the reaction of 3 with 1b is not a simple alkyne adduct (cf. the platinum chemistry described above) but rather an unexpected binuclear selenoacyl complex, [MoRh(μ^-SeCCtCSiMe3)Cl(CO)2(PPh3){HB(pzMe2)3}] (2, Scheme 1).16 Complex 2 was obtained in surprisingly high yield (63%), which given the complexity of the transformations perhaps argues for an intramolecular sequence. The ESI-mass spectrum, while devoid of peaks due to the molecular ion, does include abundant peaks that on the basis of isotopic simulation are consistent with sequential loss of chloride and one or two carbonyl ligands. The infrared spectrum (CH2Cl2) has two (12) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem. Soc. A 1966, 1711. (13) (a) Mague, J. T.; Wilkinson, G. J. Chem. Soc. A 1966, 1736. (b) Van Gaal, H. L. M.; Graef, M. W. M.; Van der Ent, A. J. Organomet. Chem. 1977, 131, 453. (14) (a) Scheller, A.; Winter, W.; M€ uller, E. Justus Liebigs Ann. Chem. 1976, 1448. (b) M€uller, J.; Akhnoukh, T.; Gaede, P. E.; Guo, A.-L.; Moran, P.; Qiao, K. J. Organomet. Chem. 1997, 541, 207. (c) M€uller, E. Synthesis 1974, 11, 761. (d) M€uller, E.; Winter, W. Justus Liebigs Ann. Chem. 1974, 1876. (15) Caldwell, L. M.; Edwards, A. J.; Hill, A. F.; Neumann, H.; Schultz, M. Organometallics 2003, 22, 2531.

1528

Organometallics, Vol. 29, No. 7, 2010

strong absorptions at 1973 and 1795 cm-1, the latter being indicative of one carbonyl adopting a bridging or semibridging role, although on the 13C NMR time scale the terminal and bridging carbonyls undergo exchange (CDCl3: δC = 232.6). The intrinsic chirality of the MoRhCSe tetrahedrane results in the three pyrazole groups remaining inequivalent such that six C-CH3 resonances are observed. One of these (δH =1.70) is moved to higher field; however as revealed by the crystal structure determination discussed below, one methyl group points directly toward the carbon atom of the tetrahedrane and the first carbon of the alkynyl group, with four C-H 3 3 3 C distances averaging 2.98 A˚ presumably accounting for this chemical shift. In a similar manner the aromatic region of the spectrum is highly structured, indicating arrested rotation of the phosphine and its substituents. This includes a broad resonance to low field (δP = 7.93), which presumably corresponds to an ortho-proton that is directed toward the alkynyl group (C-H 3 3 3 C = 2.98, 3.20 A˚). As has been a recurrent problem in polynuclear chalcoacyl chemistry, the most significant 13C CSe resonance was not unambiguously identified in the 13C{1H} NMR spectrum, presumably due to its quaternary nature and multiplicity (103Rh, 31P, 77Se). However, all other data (including elemental microanalysis and mass spectrometry) attest to the gross formulation that was confirmed by a crystallographic study,17 the results of which are summarized in Figure 1 and Table 1. The molecular structure of 2 consists of a distorted tetrahedral arrangement of Mo1, Rh1, C18, and Se atoms supported by a semibridging carbonyl ligand (Rh 3 3 3 C17= 2.1928(13) A˚, Mo1-C17-O2=154.0(1), Rh1-C17-O2= 122.1(1)). The rhodium center is coordinatively unsaturated (16-electron), and if the MoCSe unit is considered as a net (16) (a) 2: A mixture of 1b (0.200 g, 0.31 mol) and 3 (0.290 g, 0.31 mmol) in dichloromethane (15 mL) was stirred for 1 h, then concentrated to ca 5 mL and chromatographed on silica gel. Elution with dichloromethane afforded first a minor brown band, which was discarded, followed by a slow moving dark red band. Once the brown side product had been removed, the eluent was changed to tetrahydrofuran, with which the complete red band was quickly eluted. The solvent was removed in vacuo and the residue crystallized from a mixture of dichloromethane and hexane. Yield: 0.215 g (65% for CH2Cl2 monosolvate). IR (CH2Cl2): 2112w (νCtC), 1972vs, 1795s (νCO), 1605m, 1545m (νCN) cm-1. 1H NMR (CDCl3, 299.9 MHz): δ 0.00 (s, 9 H, SiCH3), 1.70 (s br, 3 H, pzCH3), 2.29, 2.31, 2.34, 2.37, 2.54 (s  5, 3 H  5, pzCH3), 5.69, 5.78, 5.81 (s  3, 1 H  3, pzH), 7.37-7.75 (m, 14 H, C6H5), 7.93 (s br, 1 H, C6H5). 13C{1H} NMR (CDCl3, 75.42 MHz, RhMoSeC resonance not identified): δ -0.82 (SiCH3), 12.58, 12.91, 13.36, 14.27, 16.08, 18.99 (pzCH3), 100.0, 113.2 (CtC), 107.4, 107.6, 108.5 [C4(pz)], 128.1 - 134.8 (C6H5), 144.2. 144.5, 145.9, 152.2, 153.1, 154.4 [C3,5(pz)], 232.6 (CO). 31P{1H} NMR (121.4 MHz), CDCl3: δ 39.9 (1JRhP=197.8, 2JPSe=46.4 Hz); C6D6: δ 39.0. ESI-MS (þve ion, MeCN): m/z 974.4 [M - Cl - CO]þ, 946.4 [M - Cl - 2CO]þ. Anal. Found: C, 45.21; H, 4.72, N, 7.82. Calcd for C41H46BClMoN6O2PRhSeSi 3 CH2Cl2: C, 44.92; H, 4.31; N, 7.48. (b) Ten minutes after combining 1b and 3, the infrared absorbances for 1b (2000, 1919 cm-1) are completely replaced by two absorptions at 1977 and 1894 cm-1. The relative intensity profile of the two bands is similar to that of 1b, suggesting little variation in the geometry at molybdenum. This is consistent with this species corresponding to the appending of rhodium to the CtC bond remote from molybdenum. (17) Crystals of 2 3 CH2Cl2 suitable for diffractometry were obtained by slow evaporation of a dichloromethane solution. Crystal data: C41H46BClMoN6O2PRhSeSi 3 CH2Cl2; Mr =1122.89; triclinic; P1 (No. 2); a=9.9653(1) A˚; b=15.1096(2) A˚; c=15.8416(3) A˚; R=91.000(1); β=98.005(1); γ=100.577(1); V=2319.65(6) A˚3 ; Z=2; Dc=1.608 Mg m-3; μ(Mo KR)=1.686 mm-1; T=110(2) K, dark red prism 0.35  0.37  0.22 mm; 87 052 measured reflections, F2 refinement, R1=0.0326, wR2 =0.0686 for 18 210 independent observed absorption-corrected reflections [|I| > 2σ(|I|), 2θ e 74] out of 23 522 independent reflections, 542 parameters, CCDC 757987.

Caldwell et al.

Figure 1. Molecular structure of 2 in a crystal of 2 3 CH2Cl2 (T = 110(2) K; 70% displacement ellipsoids; solvent, phenyl groups, and hydrogen atoms omitted; carbon atoms in gray). One enantiomer is shown, the alternative being generated by crystallographic P1 (Z = 2) symmetry. Selected distances (A˚) and angles (deg): Rh1-C18 2.0222(14), Rh1-C17 2.1928(13), Rh1-P1 2.2863(4), Rh1-Cl1 2.3481(3), Rh1-Se1 2.4965(2), Rh1-Mo1 2.78114(15), Mo1-C18 2.1062(13), Mo1-Se1 2.5617(2), Se1-C18 1.9139(13), P1-Rh1-Cl1 87.696(13), C18-Rh1-Se1 48.74(4), P1-Rh1-Mo1 120.02(1), Cl1-Rh1Mo1 152.01(1), Se1-Rh1-Mo1 57.78(1), C18-Mo1-Se1 47.17(4), C18-Mo1-Rh1 46.38(4), Se1-Mo1-Rh1 55.53(1), C18-Se1-Rh1 52.58(4), C18-Se1-Mo1 53.81(4), Rh1-Se1Mo1 66.696(5). Table 1. Selected Structural Data for the MoCSe Cores of 2, 4a, and 4b Mo-C (A˚) Mo-Se (A˚) C-Se (A˚) Mo-C-Se (deg) Mo-Se-C (deg) C-Mo-Se (deg)

2

4a5a

4b5a

2.1062(13) 2.5617(2) 1.9139(13) 79.01(5) 53.81(4) 47.17(4)

1.995(3) 2.6897(4) 1.849(3) 88.7(1) 47.9(1) 43.42(8)

1.975(3) 2.6605(5) 1.866(3) 87.6(1) 47.9(1) 44.5(1)

four-electron donor to rhodium (two electrons from coordination of the ModC bond and two from the Se), the rhodium might be very loosely described as having a “conventional” d8-square-planar situation. This said, the geometry is clearly distorted, and such a simplistic perspective is of limited value, beyond electron-counting purposes. The only structural data available for selenoacyl ligands derive from the mononuclear complexes [Mo(η2-SeCR)(CO)(L){HB(pz)3}] (R=2-thienyl; L=CO 4a, CNC6H2Me3-2,4,6 4b).5 Notwithstanding the caveat that the HB(pzMe2)3 ligand has a far more cumbersome steric profile than the more compact HB(pz)3 ligand, Table 1 presents metrical parameters for the MoCSe cores of 2, 4a, and 4b, from which it would appear that coordination of the MoCSe ring to the RhCl(PPh3) fragment is accompanied by a lengthening of the Mo-C and C-Se bonds, but somewhat unexpectedly, a contraction in the Mo-Se separation. In simplistic valence bond terms, it might be argued that this is consistent with a significant contribution of the molybdaselenirene contributor (Chart 1a) to the bonding in 4a and 4b, which is compromised upon coordination to rhodium. Relative to the mononuclear examples, the Mo1-Se1-C18 and C18-Mo1-Se1 angles are marginally opened, while the

Communication

Organometallics, Vol. 29, No. 7, 2010

1529

Mo1-C18-Se angle is significantly contracted (ca. 9), reflecting the shorter Mo1-Se1 separation. The mechanism by which 2 forms is open to conjecture in the absence of definitive spectroscopic data for any intermediates.16b However, some precedent is available in support of the mechanism suggested in Scheme 1, notwithstanding that for intermediates the actual number of coordinated phosphine ligands is indicated without any great conviction and no evidence. Despite the presence of potentially three equivalents of phosphine, no triphenylphosphine selenide was identified in the 31P{1H} NMR spectrum of the reaction mixture. Phosphines are comparatively efficient traps of the heavier chalcogens, dating back to Wilkinson’s archetypal thiocarbonyl synthesis of [RhCl(CS)(PPh3)2] from [RhCl(PPh3)3], CS2, and PPh3.1,19 The use of phosphines to abstract selenium from coordinated carbon diselenide20 and carbon selenidesulfide21 has also been applied to chalcocarbonyl synthesis, the latter demonstrating that it is the C-Se rather than C-S bond that is the more reactive. We are therefore inclined to suspect that the mechanism does not involve the liberation of free selenium but rather involves a linear succession of intramolecular processes, which also accounts for the respectable yield. We therefore contend that following initial π-coordination of the CtC bond to rhodium16b (the initial site of attack by cobalt carbonyl9a and zerovalent platinum9b), insertion of the rhodium(I) into the alkynyl C-Se bond provides the isoselenocarbonyl species A. These steps are akin to those observed for the reaction of 1a with [Pt(η2-C2H4)(PPh3)2],9b i.e., formally an oxidative addition of the rhodium(I) center. An iridium isoselenocarbonyl complex has recently been implicated in the synthesis of the unusual carbido complex [Ir2(μ^-Se2)(CtMo(CO)2{HB(pzMe 2 )3 }2 )(CO)2 (PPh 3 )2 ] from [Ir(NCMe)(CO)-

(PPh3)2]BF4 and [Et4N][Mo(CSe)(CO)2{HB(pzMe2)3}].22 The intimate details of the conversion of A to the final product 2 remain highly speculative; however Angelici and Stone have reported the crystal structures of binuclear thiocarbonyl complexes [WM( μ-CS)(CO)2{HB(pz)3}Ln] (MLn=AuPPh3, Mo(CO)2(η5-C9H7)), in which the thiocarbonyl bridge is similar to that depicted for B.23 The subsequent conversion of B to C is effectively a migratory insertion of the alkynyl group to the selenocarbonyl bridge, which depletes the valence electron count of rhodium so as to allow condensation (Mo-Rh bond formation) of the cage structure with formation of 2. Steric factors notwithstanding, and these are significant for the HB(pzMe2)3 ligand,18 none of these steps would appear to involve especially large molecular rearrangements and might well proceed in a concerted manner, thereby accounting for the failure to observe any intermediates. Nevertheless, the facility with which these rearrangements occur (room temperature) is noteworthy and attests to the lability of C-Se bonds in these systems.

(18) (a) Trofimenko, S. Scorpionates: The Coordination of Polypyrazolylborate Ligands; Imperial College Press: London, 1999. For recent reviews on organometallic chemistry supported by poly(pyrazolyl)borate ligands see ref 10c and (b) Lail, M.; Pittard, K. A.; Gunnoe, T. B. Adv. Organomet. Chem. 2008, 56, 95. (c) Becker, E.; Pavlik, S.; Kirchner, K. Adv. Organomet. Chem. 2008, 56, 155. (d) Crossley, I. R. Adv. Organomet. Chem. 2008, 56, 199. (19) Baird, M. C.; Wilkinson, G. Chem. Commun. 1966, 267. (20) Butler, I. S.; Cozak, D.; Stobart, S. R. Inorg. Chem. 1977, 16, 1779. (21) Kolb, O.; Werner, H. J. Organomet. Chem. 1984, 268, 49.

Supporting Information Available: Full details of the crystal structure determination of 2 3 CH2Cl2 (CCDC 757987) in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

The “RhCl(PPh3)y” (y=1-3?) scaffold clearly provides a versatile stage for molecular transformations involving C-chalcogen bond activation processes. The isolation of 2 provides further circumstantial evidence to suggest that alkynyl selenoether linkages are remarkably fragile in combination with late transition metal centers.

Acknowledgment. We thank the Australian Research Council (ARC) for financial support (Grant Nos. DP0771497, DP0881692) and the Deutscher Akademischer Austauschdienst for the award of a postdoctoral fellowship (to J.W.).

(22) Cade, I. D.; Hill, A. F.; McQueen, C. M. A. Organometallics 2009, 28, 6639. (23) (a) Doyle, R. A.; Daniels, L. M.; Angelici, R. J.; Stone, F. G. A. J. Am. Chem. Soc. 1989, 111, 4995. (b) Kim, H. P.; Kim, S.; Jacobson, R. A.; Angelici, R. J. J. Am. Chem. Soc. 1986, 108, 5154.