Organometallics 1993,12, 4334-4341
4334
Thermally Stable Aryltungsten(V1) Oxo and Phenylimido Complexes Containing Phenyl Ligands with ortho-Chelating Tertiary Amine Substituents: Molecular Structures of W[( R )-Cs&CH( Me)NMe2-2]C13(=0) and W(C6H4CH2NMe2-2)Cl2(=NPh)(OCMe3) Paul A. van der Schaa€,t Jaap Boersma: Huub Kooijman,t Anthony L. Spek,t and Gerard van Koten*J Department of Metal-Mediated Synthesis, Debye Institute, and Laboratory of Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands Received March 4, 199P Thermally stable aryltungsten(VI) oxo and phenylimido complexes have been synthesized using phenyl ligands with ortho-chelating CH2NMe2, CH(MeINMe2, and CH2OMe substituents. By a combination of the stabilizing features of the ortho-chelating phenyl ligands with those of tert-butoxide ligands, aryltungsten(VI) phenylimido complexes have been obtained which are not only surprisingly thermally stable (up to a t least 140 "C) but also stable toward air and water. The solid-state structuresof two of these complexes, W [(R)-C&CH(Me)NMe2] C h ( 4 ) (lb) and W(C&IICH~NM~~-~)C~~(=NP~)(OCM~~) (5) have been investigated. Crystals of lb are monoclinic, space group P21, with unit-cell dimensions a = 8.182(1) A, b = 12.100(1) A, c = 13.885(1) A, B = 90.04(1)", V = 1374.6(2) A3,Z = 4, final R = 0.033, and R, = 0.041 for 4561 reflections with I > 2.5a(I) and 308 parameters. Crystals of 5 are monoclinic, space group P21/n, with unit-cell dimensions a = 9.0035(5) A, b = 25.182(1) A, c = 9.3131(5) A, = 97.621(4)OYV = 2092.9(2) A3,Z = 4, final R = 0.047, and R, = 0.040 for 2785 reflections with I > 2.5u(I) and 228 parameters. Both complexes are monomeric, octahedral species which are six-coordinated as a result of intramolecular amine coordination (in a trans position relative to the oxo group in l b and the phenylimido group in 5). These aryltungsten(V1) complexes are six-coordinate in solution both a t ambient and at elevated temperatures. Introduction
Recently, we published the synthesis of a series of thermally stable aryltantalum(V) complexes in which the strategy of using intramolecular coordination of tertiary amines was successfully applied.' The presence of a chelatingarylamine ligand not only stabilizesthe resulting organotantalum(V) complexes but is also responsible for an interestingintramolecular aminomethyl C-H activation reaction, which results in the formation of an alkane and an intramolecularly bonded tantala(V)azacyclopropane species. We were interested whether similar effects could occur in corresponding high-valent organotungsten complexes. Therefore, we set out to study the accessibility and stability of such aryltungsten(V1) complexes and to use the results in the design of tungsten(V1) alkylidene
* To whom correspondence should be addressed.
Debye Institute. Bijvoet Center for Biomolecular Research. Abstract published in Aduance ACS Abstracts, September 15,1993. (1) Abbenhuis, H.C. L.; Grove, D. M.; Van Mier, G. P. M.; Spek, A. L.; Van Koten, G. J. Chem. SOC.,Chem. Commun. 1989, 1581. (b) Abbenhuis, H.C. L.; Grove, D. M.; Van Mier, G. P. M.; Spek, A. L.; Van Koten, G. Reel. Trau. Chim. Pays-Bas 1990,109,361. (c) Abbenhuis, H. C. L.; Grove, D. M.; Van der Sluis, P.; Spek, A. L.; Van Koten, G. Reel. Trau. Chim. Pays-Bas 1990,109,446. (d) Abbenhuis, H. C. L.; Feiken, N.; Haarman, H.F.; Grove, D. M.; Horn,E.; Kooijman, H.; Spek, A. L.; Van Koten, G. Angew. Chem.,Znt.Ed. Engl. 1991,30,996. (e) Abbenhuis, H. C. L.; Feiken, N.; Grove, D. M.; Jastnebski, J. T. B. H.;Kooijman, H.; Van der Sluis, P.; Smeets, W. J. J.; Spek, A. L.; Van Koten, G. J. Am. Chem. Soc. 1992, 114, 9773. (0Abbenhuis, H.C. L.; Van Belzen, R.; Grove,D.M.;Klomp,A.J. A.;VanMier, G.P. M.;Spek, A.L.;VanKoten, G. Organometallics 1993, 12, 210. t
8
d
~
~
eMe
\ / __. \ / --a
6
2
\ / ...
b
C
Me
0
~
.
\ / -.d
Figure 1. Selected bidentate, monoanionic aryl ligands.
complexes for olefin metathesis and ring-opening metathesis polymerization reactiom2 We here report the synthesis and characterization of a series of stable, monomeric aryltungsten oxo and phenylimido complexes, containingpotentially bidentate aryl ligands (cf. Figure 1). The selected bidentate, monoanionic ligands possess an anionic ipso-carbon atom and either a tertiary amine (a-c) or an ether oxygen atom (d) as ligating sites. Ligand b contains a stereogenic benzylic center which provides a unique NMR probe3s4for the detection of W-N coordination. The ortho-methyl-containingligand c is of interest because it lacks &hydrogen atoms. Its methyl group may interfere, for example via yelimination reactions, with other ligands present in the tungsten coordination sphere. In ligand d the dimethylaminogroup is replaced by a more weakly donating methoxy group. (2) Preliminary results have been reportad: Van der Schaaf, P. A.; Smeets, W. J. J.;Spek, A. L.;Van Koten,G.J. Chem.SOC.,Chem.Commun. 1992,717. (3) Van de Ploeg, A. F. M. J.; Van der Kolk, C. E. M.; Van Koten,G. J. Organomet. Chem. 1981,212, 283. (4) Van Koten, G.; Jastnebski, J. T. B. H.;Noltes, J. G.; Pontenagel, W. M. G. F.; Kroon, J.; Spek, A. L. J. Am. Chem. SOC.1978,100,6021.
0276-7333/93/2312-4334$04.00/00 1993 American Chemical Society
Organometallics, Vol. 12, No. 11, 1993 4336
Aryltungsten( VI) Oxo and Phenylimido Complexes Scheme I
&in$ R
in Et20; -2 LiCl 0 'C,
R' Y
R'
ambient temperatures. Surprisingly, l b tolerated refluxing in toluene under a nitrogen atmosphere for a t least 1 week, whereas 2 and 4 slowly decompose in solution under an inert atmosphere at 80 "C. Even 3c, containing an o-Me group, does not decompose via a y-elimination reaction, which is known to be a common decomposition pathway for o-Me-containing ligands in both early-9 and late-transition-metal chemistry.1° The stability of the aryltungsten(V1) complexes does not change significantly when the oxo group is replaced by a phenylimido group. However, when a tert-butoxy group, which is a good a donor, is attached to the tungsten center, as in 5, the stability is enhanced dramatically. For example, 5 can be handled in air, and the data collection for an X-ray diffraction study (vide infra) could be performed in air without taking special precuations; however, for longer periods it is advisable to store 5 under an inert atmosphere. Complex 5 slowly decomposes upon heating in air (dec pt -145 "C). Complexes 6a,b, containing two tert-butoxy groups, are very air stable, even for longer periods. For example, 6b can be melted in air without decomposition (mp 138 "C), and even addition of water to a solution of 6b, at 300 K, in toluene-k8 does not lead to decomposition. Solutions of 7a,b, which, besides two tert-butoxy groups, contain a (trimethylsily1)methyl group, are thermally stable under an inert atmosphere up to at least 80 "C but slowly decompose upon exposure to air. Structures of the Aryltungsten(V1) Complexes 1-7 in the Solid State a n d i n Solution. S o l i d - s t a t e Structures. To elucidate the stereochemistry of these complexes and to have direct proof for the intramolecular coordination of NMe2 group, X-ray structure determinations were carried out on W [(R)-CeH&H(Me)NMez2lCb(=O) (lb) and W(C6H4CHzNMez-2)Clz(=NPh)(OCMe3) (5). Suitable crystals were obtained by cooling saturated hexane solutions of l b and 5 to -30 "C. The asymmetric unit in the crystal structure of l b contains two independent molecules which are chemically identical but which differ slight, although not significantly, in structure. Figure 2 shows the ORTEP drawings of l b and 5 together with the adopted numbering schemes. The atomic coordinates for the molecules,as well as the selected bond distances and angles, are given in Tables I-IV. The tungsten atoms in both complexes are six-coordinate. In lb, Cipo and the three chlorine atoms lie in one plane, and in 5, the same is true for Cipo, two chlorine atoms, and the tert-butoxide group. Intramolecular W-N coordination occurs in both complexes with the N atom trans to the oxo oxygen in l b and trans to the imido tungsten in 5. The resulting W-C-C-C-N chelate rings are slightly puckered. The W-N bond lengths in l b and 5 are different, Le. 2.499(7) and 2.476(7) A for both residues in l b (average 2.487(5) A) and 2.420(8) A in 5, but both lie in the range of W-N,2 Ta-N,' and Sn-N4 bond lengths in complexes with this type of chelating ligand. They also are close to the bond lengths of a tungsten(V1) tmeda complex, which, to our knowledge, is the only example of a tertiary amine
R
Finally, it is well-documented that improved stability toward intramolecular decomposition pathways, e.g. 8elimination, can be achieved by using more strongly a-electron-donating ligands, such as the phenylimido group instead of the oxo group, and by introducing hard alkoxide ligand^.^ Therefore, derivatives of W(C6H4CH2NMe2-2)Cl3(=NPh) (3a) have been prepared, and characterized, in which the chlorides are successively replaced by tertbutoxy groups.
Results Synthesis and Stability of the Aryltungsten(V1) Complexes. The new aryltungsten(V1) oxo and phenylimido complexes 1-6 have been prepared via metalation of the starting tungsten chloride complex with the diarylzinc derivative (ZnAr2) of the corresponding ligand. These diarylzinc compounds were prepared from the corresponding aryllithium compound and zinc dichloride (see Scheme I). Bis[2-(methoxymethyl)phenyl] zinc, the diarylzinc compound derived from d, is new, while the diarylzinc compounds derived from a-c have been reported before.lf~6t7 For 1-4, the synthesis was carried out using a diethyl ether suspension of tungsten oxo or phenylimido tetrachloride at low temperature. Complexes 5 and 6 were prepared in CH2Clz at 0 "C, using the anionic tungsten chloride complex [WCld=NPh)(OCMe3),1 [NE41 ( x = 1and 2, respectively). These anionic tungsten chlorides are easily accessible and are stable toward intramolecular decomposition.8 The alkyl complexes 7a,b were prepared by adding 1 equiv of LiCHzSiMes to a benzene solution of 6a,b, respectively (see Scheme 11). Initial attempts to prepare the described aryltungsten(VI) complexes 1-6 involved reactions of the tungsten chlorides with the more easily accessible organolithium or Grignard reagents. None of these reactions afforded an isolable aryltungsten(V1) complex, but unidentifiable products were obtained, most probably due to the greater reactivity of lithium and magnesium compounds in substitution and reduction reactions of metal halides. Complexes 1-4 were obtained as dark, moisture- and air-sensitive solids which decompose rapidly in air but are stable for several months under an inert atmosphere at (5) (a) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkorides; AcademicPress: London, 1978. (b)Nugent, W. A.;Haymore,B.L. Coord. Chem. Rev. 1980, 31, 123. (c) Chisholm, M. H.; Rothwell, I. P. In Comprehensiue Coordination Chemistry; Wilkinson, G.,Ed.; Pergamon Preas: Oxford, U.K., 1987;Vol. 2. (d) Nugent, W. A.;Mayer,J. M. MetalLigand Multiple Bonds;Wiley New York, 1988. (6) Budzelaar,P. H. M.;Alberta-Jansen, H.-J.;Mollema, K.; Boersma, J.;VanderKerk,G.J.M.;Spek,A.L.;Duisenberg,A. J.M.J.Organomet. Chem. 1983,243,137. (7) Oeman, A.; Steevensz, R. G.;Tuck, D. G.; Meinema, H. A.; Noltes, J. G. Can. J. Chem. 1984, 62, 1698. (8) Pedersen, S. F.; Schrock, R. R. J. Am. Chem. SOC.1982,104,7483.
~
~~
~~
~
(9) Sharp, P. R.; Astmc, D.; Schrock, R. R. J. Organomet.Chem. 1979, 182,477. (10) (a) VanderZeijden,A.A.H.;VanKoten,G.;Luijk,R.;Nordemann, R. A.;Spek,A. L. Organometallics 1988,7,1549. (b)Farmetti, E.;Nardm, G.; Graziani, M. J. Chem. SOC.,Chem. Commun. 1989,1284.
van der Schaaf et al.
4336 Organometallics, Vol. 12, No. 11, 1993 Scheme I1
-
x= 0
l a R = R = H;Y NMe2 l b R Me;R = H; Y I NMe,
OEt2
2 R=R-H;Y=OMe X = NPh
+ '12 ZnAr2
- V2 ZnCI,
3e R = R ' = H; Y I N M e 3b R =Me;R ' = H;Y I NMe, 3c R = H; R = Me;Y = NMe, 4 R=R'=H;Y=OMe
6a or 6b
C&
-
+-LiCH2SiMe3 LiCl a,#L%zMe3 MqCO
7bR-Me
I
coordinating to a tungsten(V1) center.'l The R configuration of the benzylic carbon atom in l b could be unambiguously established and is in accord with the configuration of the starting (R)-a-methylbenzylamine. Structures i n Solution. The aryltungsten(V1)complexes 1-7 can be either five- or six-coordinatedepending on whether intramolecular coordination of the amino group, for ligands a-c, or methoxy group, for ligand d, occurs. Some relevant lH and 13C NMR data are given in Tables V and VI, respectively. The possibilityof detecting W-N or W-O dative bonding in solution by NMR spectroscopy depends on the ligand arrangement in the complexes. When the molecule contains a plane of symmetry that also contains the benzylic carbon center and/or the amine nitrogen center, W-N coordination cannot be established. Although the chemical shifts of the NMez and OMe groups in these complexesdo not allow conclusions to be drawn about the presence of W-N and W-O coordination, they do suggest that all resonances are shifted significantly to lower field with respect to those in the free ligand (A6 = 0.76for the NMez group and A6 = 0.85 for the OMe group relative to the free ligands in the same solvent). Moreover, the resonance of the NMez group shifts to higher field when the chlorine atoms in the aryltungsten phenylimido complexes are successivelyreplaced by tert-butoxy groups (Ab = 0.1 per OCMes group). This substituent effect on the NMe2 chemical shift does suggest that W-N coordination occurs in these complexes. A similar trend is observed for 2 and 4,derived from ligand d. With ligand b, containing a chiral benzylic carbon atom, a stereogenic center is introduced. All complexes containing this ligand show diastereotopicity for the NMez groups, which unambiguously demonstrates that also in Solution W-N coordination is present (on the NMR time ~ c a l e ) . ~ (11)(a) Churchill,M.R;Ziller, J. W.;Pederson, S. F.; Schrock, R. R. J. Chem. SOC.,Chem. Commun. 1984,485. (b)Schrock, R. R.; Pederson, S. F.; Churchill, M. R.; Ziller, J. W.Organometallics 1984,3,1574.
7aR-H
Discussion The present results show that stable aryltungsten(V1) complexes are easily accessible when phenyl ligands are used which contain a potentially coordinating group. With these types of ligands even simple aryltungsten(V1) oxo and phenylimido trichlorides show very good thermal stability, when compared with most of the earlier reported aryltungsten complexes.12 The first examples of aryltungsten(I1) complexes with intramolecular coordination were reported recently, viz. divalent complexes prepared by oxidative-additionreactions of benzylideneamineawith zerovalent tungsten c0mp1exes.l~To our knowledge,just one thermally stable aryltungsten(V1) complex has been reported (which is stabilized by a terdentate tris(3,5dimethylpyrazoly1)borateligand).14 As expected, the stability of aryltungsten phenylimido trichlorides can be further enhanced by replacing the chloride anions by strong r-electron-donor substituents, such as tert-butoxides, which render the metal center less electron deficient. The r-electron-donating capacity of the tert-butoxide ligand is reflected in the NMR data for complexes 5 and 6. When in these complexesthe chemical shift of Cjpo of the chelating ligand is compared with those of complexes 3, in which tert-butoxy groups are absent, the resonance for Cjpao is shifted to higher field (see Table (12)(a)Funk,H.;Hanke, W. Angew. Chem. 1959,71,408.~b) Sarry, B.;Detkke, M.;Growmann, H. 2.Anorg. Allg. Chem. 1964,329,218.(c) Thiele, K.-H.; Grahlert, W. Z.Chem. 1969,9, 310. (d) Grahlert, W.; Thiele, K.-H. 2. Anorg. Allg. Chem. 1971,383, 144. (e) Kinsella, E.; Smith, V. B.; W y , A G. J. Organomet.Chem. 1972,34,181.(0Thiele,
K.-H. Pure Appl. Chem. 1972,30,575. (13)(a) Richmond, T. G.; Oatarberg, C. E.; Arif,A. M.J. Am. Chem. Soc. 1987,109,8091. (b) Richmond, T. G.; King, M.A.; Keleon, E. P.; Arif,A. M.Organometallics 1987,6,1995.(c) &tarberg, C. E.; Arif,A. M.; Richmond, T. G. J. A M . Chem.SOC.1988,110,6903.(d) Pow,M. J.;Arif, A. M.;Richmond,T. G. Organometallics 1988,7,1669.(e)Lucht, B. L.;P w ,M.J.; King, M. A.; Richmond, K. G. J. Chem. SOC.,Chem. Commun. 1991,400. (14)Eagle, k A.;Tiekink, E. R. T.;Young,C. G. J. Chem. SOC.,Chem. Commun. 1991,1746. (15)Gibeon, V. C.; Kee, T. P.; Shaw, A. Polyhedron 1988,7,579.
Organometallics, Vol. 12, No.11, 1993 4337
Aryltungsten(VI) Oxo and Phenylimido Complexes Table I.
Fractional Coordinates and Equivalent Isotropic Thermal Paramem for
W I ( R ) - C ~ ~ ( M e ) N 2 ~ (3l b() ~ ) X Y z Uq,A'
UI
C13 10
c9
0.20102(4) 0.0288(10) 0.4665(9) 0.6742(13) 0.2348(11) 0.1149(13) 0.1334(13) 0.2822( 14) 0.4107(12) 0.3909(12) 0.5305(11) 0.5897( 13) 0.4331(13) 0.3686(5) 0.2555(4) 0.0684(3) 0.28348(4) 0.4840(9) 4.0069(9) -0.1748(13) 0.2579(12) 0.3908(12) 0.3765( 14) 0.2378(14) 0.1180(15) 0.1264( 11) -O.OO69( 12) 4).0964(16) -0.0998(13) 0.2952(5) 0.1935(5) 0.2304(5)
1.0031(3) 0.941 l(7) 1.0520(6) 0.9560(10) 0.8855(8)
0.8168(10) 0.7424(10) 0.7352(10) 0.8024(9) 0.8784(8) 0.9439(8) 1.1015( 10) 1.1290(8) 0.8981(3) 1.1533(3) 1.1 18l(3) 0.14603(4) 0.1589(9) 0.1493(7) 0.2144(12) 0.2655(10) 0.3437(10) 0.4216( 11) 0.4231(11) 0.3482(10) 0.2705(9) 0.1817(8) 0.0417(11) 0.2342(9) 0.0019(3) 0.0235(3) 0.2843(3)
0.01249(2) 0.0530(5) -0.0642(5) -0.1732(9) -0.0983(6) -0.1268(8) -0.1990(7) -0.2468(7) -0.2207(6) -0.1461(7) -0.1034(7) -0.0005(9) -0.1461(8) 0.1123(2) 0.1082(3) -0.0921 (2) 0.49399(3) 0.4787(8) 0.5440(6) 0.6861(8) 0.5999(8) 0.6169(8) 0.6886(8) 0.7456(7) 0.7347(7) 0.6605(7) 0.6462(7) 0.5363(10) 0.4867(7) 0.6025(3) 0.3754(2) 0.3844(2)
0.0403(1) 0.080(3) O.OSO(3) 0.078(5) 0.045(3) 0.069(4) 0.064(4) 0.061)(4) 0.050(3) 0.046(3) 0.051(3) 0.073(4) 0.066(4) 0.0792(10) 0.0864(11) 0.0765(10) 0.0491(2) 0.108(4) 0.055(3) 0.075(4) 0.056(4) 0.062(4) 0.076(5) 0.077(5) 0.070(4) 0.048(3) 0.061(3) 0.088(5) 0.067(4) 0.1003(13) 0.0868(13) 0.0848( 11)
Table II. Selected Geometrical Data for W[(R)-CdWWMe)NMe2-2lCM+N (Ib)
residue 1
c4
Figure 2. ORTEP drawings (30% probability level) of lb (top;one residue is shown) and 5 (bottom;H atoms are omitted for clarity) with the adopted numbering schemes.
VI). We also note that lJwc increases with increasing numbers of tert-butoxy groups. This increase suggests that the W-Ci,,, bond acquires a larger s-orbital contribution. However this effect is not reflected in the W-Cipo bond lengths for the two aryl groups in the solid-state structures; 2.091(9) and 2.073(2) A for l b and 2.137(11) A for 5, which differ less than the s u m of their 3a values. The *-donating properties of the phenylimido and tertbutoxy groups l b and 5 are reflected in the opening of the W-N-C and W-0-C angles around the imido nitrogen to 170.4' and around the tert-butoxy oxygen to 145.4'. Surprisingly, the W-N bond in the phenylimido complex 5 is significantlyshorter than this bond in the oxo complex lb, with lengths of 2.420(8) and 2.487(7) A, respectively. If this shortening is discussed in terms of trans influence of the oxo and imido ligands, it would mean that the oxo ligand is a better electron donor than the phenylimido group, in contrast with claims in the literature.6b However, it must be noted that substitution of a chloride by a tertbutoxy group in an equatorial position may also influence, both sterically and electronically, the bond lengths of the ligands in the apical positions. Interestingly, the substituent effect of the number of tert-butoxy groups is also observed for other resonances in the 'H NMR data for compounds 3-7 (see Table VI.
residue 2
W(l)-C(11) W(l)-Cl(ll) W( l)-Cl( 12) W( l)-Cl( 13) W(1)-0( 1) W(l)-N(l)
Bond Lengths (A) 2.091(9) W(2)-C(21) W(2)-C1(21) 2.308(4) W(2)-C1(22) 2.322(4) W(2)-C1(23) 2.305(3) 1.678(8) W(2)-0( 2) 2.499(7) W(2)-N(2)
2.073( 12) 2.307(4) 2.334(3) 2.307( 3) 1.662(7) 2.476(7)
N(1)-W(l)-O( 1) N(1)-W(l)
