Group VI Metal Carbonyl Complexes of Bis((diphenylphosphino)methyl)diphenylborate and an Assessment of Their Utility for Template Ligand Syntheses

Zerovalent group VI metal chemistry of anionic bis­((diphenylphosphino)­methyl)­diphenylborate (Ph2BP2) offers some surprises in comparison to the chemistry of analogous complexes of neutral bidentate phosphines. The enhanced donor ability of Ph2BP2 relative to related bis-PPh2 ligands is confirmed by IR spectral analysis of [ASN]­[M­(CO)4(Ph2BP2)] (ASN = 5-azoniaspiro[4.4]­nonane; M = Cr, Mo, W). The mononitriles [ASN]­[fac-M­(CO)3(RCN)­(Ph2BP2)] (M = Cr, R = Me; M = Mo, R = Et; M = W, R = Et) are useful reagents for the introduction of sulfur dioxide and isocyanides to the π-basic M­(CO)3(Ph2BP2) fragment. While the fundamental coordination chemistry of this anionic fragment mostly mirrors that of its conventional neutral cousins, the electronic impact of Ph2BP2 leads to divergent reactivity in some cases. For example, the sulfur dioxide complexes [ASN]­[mer-M­(CO)3(SO2)­(Ph2BP2)] (M = Mo, W) are unreactive toward CH2N2, dramatically different from the case for mer-M­(CO)3(SO2)­(L2) (L2 = dppm, dppe, dppp). The spectral data of [ASN]­[Mo­(CO)3(CNC6H4(2-NH2))­(Ph2BP2)] and [ASN]­[Mo­(CO)3(CNCH2CH2NH2)­(Ph2BP2)], salts containing the first anions of 2-aminophenyl isocyanide and 2-aminoethyl isocyanide, respectively, indicate that the anionic M­(CO)3(Ph2BP2) fragment may be more useful than neutral M­(CO)3(dppe) for the π-back-bonding induced stabilization of ligands prepared via template syntheses.