CARBONYLATION OF [TERT-BU3SINH]3ZRH AND X-RAY STRUCTURAL STUDY OF [TBU3SINH]3ZRCH3

Treatment of ZrCl4 with 3 equiv of (t)Bu3SiNHLi afforded ((t)Bu3SiNH)3ZrCl (1); alkylation of 1 with MeMgBr gave ((t)Bu3SiNH)3ZrMe (2), whose structure was determined via X-ray crystallography. Crystal data: monoclinic, P2(1)/c,a = 22.052 (3) angstrom, b = 12.943 (2) angstrom, c = 17.320 (2) angstrom, beta = 108.93 (1)-degrees, Z = 4, T = 25-degrees-C. The methyl derivative 2 exhibits near-tetrahedral coordination with a normal Zr-C distance (2.231 (7) angstrom) and virtually indistinguishable amido groups (d(Zr-N)(av) = 2.039 (7) angstrom, angle(Zr-N-Si) av = 151.4 (8)-degrees. Upon thermolysis of 2 in cyclohexane (95-degrees-C, 8 h), CH4 was eliminated via abstraction of an amido hydrogen, generating the transient [((t)Bu3SiNH)2Zr = NSi(t)Bu3] (3), which was scavenged by H2 (3 atm) to produce ((t)Bu3SiNH)3ZrH (4). The monohydride 4 was shown to reduce CO to provide [((t)Bu3SiNH)3Zr]2(mu-OCH2) (6), presumably via monohydride (4) reduction of undetected [((t)Bu3SiNH)3Zr(CHO)] (5). Further carbonylation yielded the spectroscopically observable [((t)Bu3SiNH)3Zr]2(mu-eta-1:eta-2-OCH2C=O) (7) and, ultimately, [((t)Bu3SiNH)3Zr]2(cis-mu-O(H)C = C(H)O) (8). Thermolysis of 6 in THF resulted in the elimination of ((t)Bu3SiNH)3ZrOMe (10), leaving the transient 3, which was trapped by solvent to give ((t)Bu3SiNH)2-(THF)Zr = NSi(t)Bu3 (9). The addition of LiOMe to 1 provided an alternate route to 10. The mechanism of CO reduction is discussed in relation to other group 4 and actinide mono- and dihydride systems.