Inductive modulation of tris(phosphinomethyl)phenylborate donation at group VI metals via borate phenyl substituent modificationElectronic supplementary information (ESI) available. CCDC 1824309-1824325. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt00703a

A series of zerovalent group VI metal complexes of tris(diisopropylphosphinomethyl)phenylborate ([PhB(CH 2 P i Pr 2 ) 3 ] − , PhBP iPr 3 ), including [PPN][M(CO) 3 (PhBP iPr 3 )] (M = Cr, Mo, W) and the first bimetallics in which PhBP iPr 3 serves as a bridging ligand via binding M(CO) 3 units at the three phosphorus atoms and the borate phenyl substituent, have been synthesized and fully characterized. Two new tris(phosphinomethyl)borates featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents were prepared as crystallographically characterized thallium salts, and metallated giving their inaugural transition metal complexes [PPN][M(CO) 3 (((3,5-Me)C 6 H 3 )BP Ph 3 )] and [PPN][M(CO) 3 (((3,5-CF 3 )C 6 H 3 )BP Ph 3 )]. A comparative ν (CO) infrared spectroscopic analysis and examination of half wave potentials assessed by cyclic voltammetry supports a ligand donor ranking of Tp > PhBP iPr 3 ≥ Cp > PhBP Ph 3 > triphos. For these anionic complexes, in which a lower electrostatic contribution to zerovalent metal-PhBP R 3 binding is likely operative relative to that present in the zwitterionic complexes most commonly prepared with tris(phosphinomethyl)borates, PhBP R 3 ligands do not function as strongly donating scorpionates . Nevertheless, PhBP Ph 3 is a substantially stronger donor than triphos towards zerovalent M(CO) 3 ; the half wave potentials of [Et 4 N][M(CO) 3 (PhBP Ph 3 )] are ∼340 mV lower than those of M(CO) 3 (triphos). The potentials of the ((3,5-Me)C 6 H 3 )BP Ph 3 group VI metal tricarbonyl anions are more negative than those of the corresponding ((3,5-CF 3 )C 6 H 3 )BP Ph 3 group VI metal tricarbonyl anions by ∼50 mV, suggesting a modest, yet rational, tuning of PhBP Ph 3 donation via inductive modulation of the borate anion charge. New tris(phosphinomethyl)phenylborate ligands were synthesized to examine tuning of PhBP Ph 3 donation via inductive modulation of the borate charge. Cyclic voltammetry suggests that rational tuning of this type occurs in complexes of zerovalent metals.