Inductive modulation of tris(phosphinomethyl)phenylborate donation at group VI metals: Via borate phenyl substituent modification

Paul J. Fischer, Shuruthi Senthil, Jeremy T. Stephan, McKinley L. Swift, Meghan D. Storlie, Emily T. Chan, Matthew V. Vollmer, Victor G. Young

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

A series of zerovalent group VI metal complexes of tris(diisopropylphosphinomethyl)phenylborate ([PhB(CH2PiPr2)3]-, PhBPiPr3), including [PPN][M(CO)3(PhBPiPr3)] (M = Cr, Mo, W) and the first bimetallics in which PhBPiPr3 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)C6H3)BPPh3)] and [PPN][M(CO)3(((3,5-CF3)C6H3)BPPh3)]. A comparative ν(CO) infrared spectroscopic analysis and examination of half wave potentials assessed by cyclic voltammetry supports a ligand donor ranking of Tp > PhBPiPr3 ≥ Cp > PhBPPh3 > triphos. For these anionic complexes, in which a lower electrostatic contribution to zerovalent metal-PhBPR3 binding is likely operative relative to that present in the zwitterionic complexes most commonly prepared with tris(phosphinomethyl)borates, PhBPR3 ligands do not function as strongly donating scorpionates. Nevertheless, PhBPPh3 is a substantially stronger donor than triphos towards zerovalent M(CO)3; the half wave potentials of [Et4N][M(CO)3(PhBPPh3)] are ∼340 mV lower than those of M(CO)3(triphos). The potentials of the ((3,5-Me)C6H3)BPPh3 group VI metal tricarbonyl anions are more negative than those of the corresponding ((3,5-CF3)C6H3)BPPh3 group VI metal tricarbonyl anions by ∼50 mV, suggesting a modest, yet rational, tuning of PhBPPh3 donation via inductive modulation of the borate anion charge.

Original languageEnglish (US)
Pages (from-to)6166-6176
Number of pages11
JournalDalton Transactions
Volume47
Issue number17
DOIs
StatePublished - 2018

Bibliographical note

Funding Information:
The National Science Foundation (CHE-1464515) and the Henry Dreyfus Teacher-Scholar Awards Program supported this research. The Bruker-AXS D8 Venture diffractometer was purchased with funding from an NSF-MRI grant (#1229400) and the University of Minnesota. P. J. F. thanks Connie C. Lu (University of Minnesota) for access to her laboratory for cyclic voltammetry, Viktor N. Nemykin (University of Manitoba) for an excellent suggestion, and Mark C. Lipke (Rutgers University) and Ted A. Betley (Harvard University) for advice regarding the PhBP3iPr synthesis. P. J. F. dedicates this manuscript to the memory of Prof. Wesley A. Pearson (1932–2017).

Publisher Copyright:
© 2018 The Royal Society of Chemistry.

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