Bisbiphenyl Phosphines: Structure and Synthesis of Gold(I) Alkene π-Complexes with Variable Phosphine Donicity and Enhanced Stability

Abstract

This paper describes the synthesis and characterization of RP­(o-biphenyl)2 phosphine ligands (where R = PhO, Ph, and t-Bu), corresponding gold­(I) chloride precatalysts, gold­(I) triflate catalysts, and gold­(I) π-complexes. All ligands and gold chlorides and three π-complexes were characterized in the solid state. The most significant differences between complexes in the solid state were varying P–Au bond lengths, a consistent reflection of the different electronic character of each phosphine. NMR spectroscopic data on enol ether π-complexes is consistent with increasing cationic character in the alkene fragment, from R = t-Bu to R = Ph and OPh. The intermolecular alkene exchange process for [LAu­(methoxypropene)]­SbF6 (L = PhO­(o-biphenyl)2P) is faster than that of the analogous complex with t-Bu2(o-biphenyl)­P, presumably due to the higher electrophilicity of the former complex. Examination of a series of vinyl silane π-complexes with triaryl phosphine ligands reveals increasing stability and ease of preparation (Ph3P < Ph2P­(o-biphenyl) < PhP­(o-biphenyl)2). These results reveal that incorporation of a second biphenyl substituent into ligand architectures allows preparation of a series of gold π-complexes with increased stability over a range of phosphine donicity.

A dicoordinate gold(i)–ethylene complex

“…1 span from 2.141 to 2.175 Å), 7 but similar to cationic dicoordinate gold( i ) π-complexes with other alkenes. 5 The C C double bond is slightly shorter than that of free ethylene (1.263(10) Å vs. 1.313 Å, respectively) 20 and significantly shorter compared to the described tricoordinate gold( i ) ethylene complexes ( cf. 1.365(15) and 1.387(5) Å in Bourissou's compounds), indicative of poor Au → ethylene π-backdonation.…”

“…Cationic, dicoordinate gold( i ) π-complexes of substituted alkenes, stabilized by monodentate N-heterocyclic carbenes (NHCs) 4 or phosphines, 5 have been isolated and characterized. However, despite significant synthetic efforts, dicoordinate ethylene complexes remain unknown.…”

The core of the matter – arene substitution determines the coordination and catalytic behaviour of tris(1-phosphanyl-1′-ferrocenylene)arene gold(i) complexes

“…Gold(I), in contrast to copper(I) and silver(I), [52][53][54] tends to be coordinated by arenes in an η 2 fashion with impact on asymmetric induction and catalyst stability. [55][56][57][58][59][60] However, more delocalised gold-π(arene) interactions are also encountered and deemed important for catalysis and crystal engineering. 50,[61][62][63][64][65] Indeed, when a slight excess of tris-phosphane 1b was reacted with [Au(η 2 -nbe) 3 ]OTf in CH 2 Cl 2 , 1 H and 31 P{ 1 H} NMR spectra of the reaction mixture ( Fig.…”

Dicoordinate Au(I)–Ethylene Complexes as Hydroamination Catalysts

“… 13 Among those, cationic dicoordinate gold(I) π-complexes of substituted alkenes and alkynes have been isolated and characterized over the last decade using phosphine or N-heterocyclic carbene ligands. 14 Chelating N- and P-based ligands have also proved useful to form tricoordinate gold π-complexes. 15 However, despite the interest in developing efficient methods for ethylene functionalization, gold(I)–ethylene complexes are quite rare; only 10 examples can be found in the literature and mainly using chelating ligands.…”