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We have found that tris(diphenylphosphinomethyl)phenylborate (PhBP3) makes stable complexes with zerovalent group VI metals of the form [Et4N][M(CO)3(PhBP3)] (M = Cr (1) , Mo (2), and W (3)). We also report the zwitterionic complex Mn(CO)3(PhBP3) (4). The apparent resistance of 2 and 3 towards two-electron oxidation by Br2 and I2 suggests that PhBP3 may not donate enough electron density to the Mo(0) and W(0) centers to replace tris(pyrazolyl)borates in zerovalent group VI metal π-basic dearomatization agents. The most remarkable finding of this work is the discovery of a new binding mode in PhBP3, in which one metal tricarbonyl fragment binds to the phosphines in a typical κ3 fashion, while another metal tricarbonyl fragment binds η6 to the borate phenyl substituent. Coordinating a metal in this way inductively decreases the amount of electron density at the phosphine-bound metal, creating a novel method for donation modulation of PhBP3 at phosphorous.
Weberg, Alexander B., "Low Valent Metal Complexes of Tris(diphenylphosphinomethyl)phenylborate: Novel Binding at the Phenyl Substituent Modulates Ligand Donation" (2015). Chemistry Honors Projects. Paper 14.
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