J. Am. Chem. Soc. 1994,116, 8804-8805
8804
Synthesis of Molybdenum Complexes That Contain Silylated Triamidoamine Ligands. A p-Dinitrogen Complex, Methyl and Acetylide Complexes, and Coupling of Acetylides
Me
SiR.
Keng-Yu Shih, Richard R. Schrock,’ and Rhett Kempe
Department of Chemistry 6-331 Massach uset ts Institute of Technology Cambridge, Massachusetts 02139 Received May 2, 1994 Tetradentate “triamidoamine” ligands of the type [(RsSiNCHzCH2)3N]3- (R3Si = Me3Si or t-BuMezSi) have been found to fwm complexes with first-row metals Ti-Fel-4 and This type of ligand forms relatively rigid distorted trigonal bipyramidal or pseudo-four-coordinate “trigonal monopyramidal” complexes in which the apical position is sterically protected to a significant degree by the R3Si groups. We have been interested in molybdenum complexes that contain triamidoamine ligands, in part in order to explore the binding and reduction of dinitrogen,and now have found conditionsthat allow some starting materials to be prepared simply, although so far in only moderate yield. The first results are reported here. They should be compared with a recent report of molybdenum complexes that contain pentafluorophenyl-substituted triamidoamine ligands8 and with reports of titanium, vanadium, and molybdenum complexes that contain the [(MeNCH2CH2)3N]3-
R’
SiMe,; R = M e (4s). Ph (4a’) SiPhMe2; R = M e (4b), Ph (4b‘), SiMe, (4b“) SiPh2Me: R = Me (4c). Ph (4c’), SiMe, (4c”)
SiMe, (Sa), SiPhMe2 (Sb)
Attempts to prepare “trigonal monopyramidal” complexes,’ M o [ ( R ~ S ~ N C H ~ C H ~so) ~far N have ] , failed. For example, only l a (25% yield) could be isolated from the reaction between MoCL(THF)3 in ether and Li3[(Me3SiNCH2CH2)3N] under dinitrogen, while the reaction between MoC&(THF)3and Li3[(tBuMezSiNCHzCH2)3N] in pentane under dinitrogen gave a paramagnetic pentane-soluble purple complex (2) in 10%yield. Reactions between MoC14(THF)2 (in THF) and the Li3[N3N] No products could be identified when the latter reaction was derivativeslz shown in Scheme 1 yield the d2 monochloro carried out under argon. An X-ray structure of 214showed it to derivatives la(26%), lb(38%),or IC(31%).*3Thesecompounds, be a pdiazenido(2-) complex of Mo(IV) (Figure 1; Table 1) or like Mo[(CaFsNCH2CH2)sNIC1,8 are paramagnetic,as evidenced alternatively, a pdinitrogen complex of Mo(II1). The Mo( 1)by broad, shifted ligand resonances. We assume that their structures are analogous to those of M o [ ( C ~ F S N C H ~ C H ~C18 ) ~ N ] N(4) bond distance of 1.907 (8) A, N(4)-N’(4) bond distance of 1.20(2) A, and Mo(l)-N(4)-N’(4) bond angle of 178(1)O are and V[(Me3SiNCH2CH2)3N]C12 and, therefore, that their all consistent with a formulation in which there is considerable paramagnetism can be ascribed to a degeneracy of the d,, and ?r delocalization. These data should be compared with the N-N dyp orbitals (taking the z axis to be the pseudo 3-fold axis). bond length [1.236(3) A] and Mo-N bond length [1.819(2) Attempts to prepare MO[(~-BUM~ZS~NCH~CH~)~N]C~ in a and 1.821(3) A] in the “hydrazido(4-)” complex, Cp*Me3similar manner so far has yielded only traces ( C=CMe > C1, and for a given X the ease of oxidation follows the trend SiR3 = SiMe3 > SiMe2Ph > SiMePh2. Preliminary studies suggest that these are one-electron oxidations and that in some cases the cations can be isolated at 25 “C. The chemistry described here is the first involvinghigh oxidation state Mo complexes that contain silylated triamidoamine ligands. We are continuing to explore the potential utility of triamidoamine ligands for organometallic chemistry and dinitrogen chemistry of the earlier, heavier transition metals in mid to high oxidation states.
steric reasons that the configuration about the C=C bond is trans, although we have no data that confirm that proposal. This coupling reaction is most closely related to that observed when d2 tantalum and niobium chlorides react with a~etonitrile,~*J~ and the products are related to those formed from alkylidyne Acknowledgment. We thank the National Institutes of Health complexes and enediynes via metathesis rea~ti0ns.l~At the (GM 31978) and the National Science Foundation (CHE 91 present time we assume that coupling of d2 acetylide complexes 22827) for supporting this research. is slow when Cb in the acetylide is substituted. Although there are many examples of acetylide couplings,20*21 we could find no Supplementary Material Available: Experimental details for other example of this “tail-to-tail” type in which each metal is selected compounds, experimental details for the structure study oxidized by two electrons in the process. of 2, an ORTEP representation of 2, and final positional and (17) Krouse, S. A.; Schrock, R. R. J. Organomet. Chem. 1988,355,257. final thermal parameters for 2 (16 pages). This material is ( 1 8 ) Finn, P. A.; King, M. S.; Kilty, P. A.; McCarley, R. E. J . Am. Chem. SOC.1975, 97, 220. contained in many libraries on microfiche, immediately follows (19) Cotton, F. A.; Hall, W. T. Inorg. Chem. 1978, 17, 3525. this article in the microfilm version of the journal, and can be (20) Evans, W. T.; Keyer, R. A.; Ziller, J. W. Organometallics 1993,12, ordered from the ACS; see any current masthead page for ordering 2618. information. (21) Shutowski, D. G.; Stucky, G. D. J. Am. Chem. SOC.1976,98,1376.
