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.