The advent of frustrated Lewis pair (FLP) chemistry almost a decade ago was based on the reactivity of sterically encumbered combinations of electrophilic boranes and phosphines with hydrogen. Since that time the chemistry has broadened dramatically in terms of reactivity and applications. Nonetheless, the majority of the work has continued to exploit the borane B(C6F5)3. In this review, we describe FLP chemistry that has developed by employing alternatives to this Lewis acid. Lewis acids derived from group 13, 14, and 15 based systems are described, thus demonstrating a growing area in the main group reactivity based on FLPs.
Silyl triflates of the form R4-n Si(OTf)n (n=1, 2; OTf=OSO3 CF3 ) are shown to activate carbon dioxide when paired with bulky alkyl-substituted Group 15 bases. Combinations of silyl triflates and 2,2,6,6-tetramethylpiperidine react with CO2 to afford silyl carbamates via a frustrated Lewis pair-type mechanism. With trialkylphosphines, the silyl triflates R3 Si(OTf) reversibly bind CO2 affording [R'3 P(CO2 )SiR3 ][OTf] whereas when Ph2 Si(OTf)2 is used one or two molecules of CO2 can be sequestered. The latter bis-CO2 product is favoured at low temperatures and by excess phosphine.
Novel
cationic E–Cl (E = Ge, Sn) fragments stabilized by
a bis(phosphino)borate ligand (2E) were synthesized by
a 1:1 stoichiometric addition of ECl2 and [Tl][(Ph2PCH2)2BPh2]. The metrical
parameters are consistent with dative bonds between the phosphorus
atoms and the electron-deficient group 14 element, which is in contrast
to the traditionally used aryl- and nitrogen-based ligands, which
are always covalently bound. The reaction of a second equivalent of
bis(phosphino)borate results
in the unexpected insertion of the main group center into the aliphatic
B–C bond of the ligand backbone to form 3E, in
addition to phosphine-borane dimer (Ph2PCH2BPh2)2 (4). The pendant phosphine on 3E was shown to possess donor ability in the coordination
of BH3 (5E).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.