Bis(phosphino)borates: A New Family of Monoanionic Chelating Phosphine Ligands

The reaction of dimethyldiaryltin reagents Me2SnR2 (R = Ph (1), p-MePh (2), m,m-Me2Ph (3), p-tBuPh (4), p-MeOPh (5), p-CF3Ph (6)) with BCl3 provided a high-yielding, simple preparative route to the corresponding diarylchloroboranes R2BCl (R = Ph (10), p-MePh (11), m,m-Me2Ph (12), p-tBuPh (13), p-MeOPh (14), p-CF3Ph (15)). In some cases, the desired diarylchloroborane was not formed from an appropriate tin reagent Me2SnR2 (R = o-MeOPh (7), o,o-(MeO)2Ph (8), o-CF3Ph (9)). The reaction of lithiated methyldiaryl- or methyldialkylphosphines with diarylchloroboranes or dialkylchloroboranes is discussed. Specifically, several new monoanionic bis (phosphino)borates are detailed: [Ph2B(CH2PPh2)2] (25); [(p-MePh)2B(CH2PPh2)2] (26); [(p-tBuPh)2B(CH2PPh2)2] (27); [(p-MeOPh)2B (CH2PPh2)2] (28); [(p-CF3Ph)2B(CH2PPh2)2] (29); [Cy2B(CH2PPh2)2] (30); [Ph2B(CH2P{p-tBuPh}2)2] (31); [(p-MeOPh)2B(CH2P{ptBuPh}2)2] (32); [Ph2B(CH2P{p-CF3Ph}2)2] (33); [Ph2B(CH2P(BH3)(Me)2)2] (34); [Ph2B(CH2P(S)(Me)2)2] (35); [Ph2B(CH2PiPr2)2] (36); [Ph2B(CH2PtBu2)2] (37); [(m,m-Me2Ph)2B(CH2PtBu2)2] (38). The chelation of diarylphosphine derivatives 25-33 and 36 to platinum was examined by generation of a series of platinum dimethyl complexes. The electronic effects of substituted bis(phosphino)borates on the carbonyl stretching frequency of neutral platinum alkyl carbonyl complexes were studied by infrared spectroscopy. Substituents remote from the metal center (i.e. on boron) have minimal effect on the electronic nature of the metal center, whereas substitution close to the metal center (on phosphorus) has a greater effect on the electronic nature of the metal center.