Alkane Binding Implicated in Reactions of (tBu3SiN═)3WHK and Alkyl Halides

Abstract

The reduction of alkyl, benzyl, allyl, and propargyl halides by [(tBu3SiN═)3WH]K (2-H-M) was assayed via analysis of the product distributions. For unhindered sp3 substrates (MeX, EtX, BnX, CH2═CHCH2X, RCCCH2X, etc.), the observed products were RH loss and [(tBu3SiN═)3WX]M (2-X-M) or MX elimination and (tBu3SiNH)(tBu3SiN═)2WR (1-R), which was derived from 1,2-RH-addition to an imide of the intermediate alkane (arene) complex (tBu3SiN═)3W(RH) (2-RH). Solvent activation or binding was also seen, consistent with the trapping of (tBu3SiN═)3W (2) generated from RH loss from 2-RH. The radical clocks cPrCH2Br and 5-hexenyl bromide yielded the unrearranged products (tBu3SiNH)(tBu3SiN═)2W(trans-c(CHCH2CHMe)) (1-cPrMe) and (tBu3SiNH)(tBu3SiN═)2W(trans-CH═CHnBu) (1-CH═CHnBu), respectively. When hindered sp3 substrates were employed, halogenated products [(tBu3SiN═)3WX]M (2-X-M) and (tBu3SiNH)(tBu3SiN═)2WX (1-X) were prominent, suggesting that radical paths were operable. KIEs derived from product ratios involving CD3I or CD3CH2I and 2-H-K supported the intermediacies of (tBu3SiN═)3W(CHD3) (2-CHD3) and (tBu3SiN═)3W(CH3CD3) (2-CH3CD3), respectively. X-ray crystal structures of (tBu3SiNH)(tBu3SiN═)2WR (1-R; R = Me, cPrMe, CH═C═CH2) are presented, and the results are placed in the context of 1,2-RH-addition to d0 early-transition-metal imido species.