Carbonylation of ( sup t Bu sub 3 SiNH) sub 3 ZrH and X-ray structural study of ( sup t Bu sub 3 SiNH) sub 3 ZrCH sub 3

Treatment of ZrCl{sub 4} with 3 equiv of {sup t}Bu{sub 3}SiNHLi afforded ({sup t}Bu{sub 3}SiNH){sub 3}ZrCl (1); alkylation of 1 with MeMgBr gave ({sup t}Bu{sub 3}SiNH){sub 3}ZrMe (2), whose structure was determined via X-ray crystallography. Crystal data: monoclinic, P2{sub 1}/c, a = 22.052 (3) {angstrom}, b = 12.943 (2) {angstrom}, c = 17.320 (2) {angstrom}, {beta} = 108.93 (1){degree}, Z = 4, T = 25C. 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){sub av} = 2.039 (7) {angstrom}, {angle}(Zr-N-Si){sub av} = 151.4 (8){degree}). Upon thermolysis of 2 in cyclohexane (95C, 8 h), CH{sub 4} was eliminated via abstraction of an amido hydrogen, generating the transient (({sup t}Bu{sub 3}SiNH){sub 2}Zr{double bond}NSi{sup t}Bu{sub 3}) (3), which was scavenged by H{sub 2} (3 atm) to produce ({sup t}Bu{sub 3}SiNH){sub 3}ZrH (4). The monohydride 4 was shown to reduce CO to provide (({sup t}Bu{sub 3}SiNH){sub 3}Zr){sub 2}({mu}-OCH){sub 2} (6), presumably via monohydride (4) reduction of undetected (({sup t}Bu{sub 3}SiNH){sub 3}Zr(CHO)) (5). Further carbonylation yielded the spectroscopically observable (({sup t}Bu{sub 3}SiNH){sub 3}Zr){sub 2}({mu}-{eta}{sup 1}:{eta}{sup 2}-OCH{sub 2}C{double bond}O) (7) and, ultimately, (({sup t}Bu{sub 3}SiNH){sub 3}Zr){sub 2}(cis-{mu}-O(H)C{double bond}C(H)O) (8). Thermolysis of 6 in THF resulted in the elimination of ({sup t}Bu{sub 3}SiNH){sub 3}ZrOMe (10), leaving the transient 3, which was trapped by solvent to give ({sup t}Bu{sub 3}SiNH){sub 2}(THF)Zr{double bond}NSi{sup t}Bu{sub 3} (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 actinide mono- and dihydride systems.