Spectroscopic and crystallographic studies of phosphino adducts of gallium(III) iodide

Abstract

The solid state structures of the compounds GaI3•PPh3 and Ga2I6•dppe ( dppe = 1,2-bis(diphenylphosphino)ethane ) have been determined. For the former, in which the GaI3P core has C3v symmetry, the structure is trigonal, with a = 14.961(2) Å, c = 16.509(3) Å, V = 3199.5(4) Å3, Z = 6, space group [Formula: see text]. In Ga2I6•dppe, the ligand bridges two GaI3P centres; the structure is monoclinic, a = 10.196(7) Å, b = 15.363(1) Å, c = 23.027(9) Å, β = 98.735(4)°, V = 3565.1(3.2) Å3Z = 4, space group P21/n The use of 31P NMR spectroscopy shows that GaI3•PPh3 is slightly dissociated in nonaqueous solution, and the effect of adding Ph3P or I− has been investigated. Similar studies with Ga2I6•dppe are also reported. In each system, four-coordination at gallium is dominant; an equally important factor is the dimerization of uncomplexed GaI3 to Ga2I6 in these solutions. Keywords: gallium(III) iodide, complexes, phosphorus, NMR, crystallography.

Lewis Acid Catalyzed Z to E Isomerization of 1,2-Bis(diphenylphosphino) ethene

“…The complex shows Q symmetry with the center of inversion located in the middle of the C=C double bond. The Ga-P distance [2.4008(2) Ä] is almost identical with literature values for R 3P-G aX3 com pounds [8,10], The GaBr3 unit is tilted towards the C=C double bond as shown by the smaller angle C l-P-G a [102.8(5)°] as compared with C211-P-Ga The crystals of compound 2 are monoclinic, space group P2i/c with Z = 4 molecules in the unit cell. Only one phosphorus atom (P 1) is coordinated to the metal atom.…”

“…Pentaor hexacoordinated intermediates as in 3, or in the transition state for the site exchange of the M 3 unit in 2 , are not likely to be relevant, as the chelat ing coordination forces the double bond into the Zconfiguration. By contrast, the coordination number of gallium and aluminium in phosphane complexes is largely limited to four [8].…”

Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

“…However, there seem to be only small effects on the Ga-E bond lengths from changing the R group, although in analogous complexes with R = aryl the Ga-E seem to be marginally longer than R = alkyl [170][171][172][173][174][175][176][177], which is in keeping both with the Ga-X bonds being dominant compared to Ga-E, and also with the absence of significant steric effects in these complexes. There appear to be no established examples of gallium(III) halide complexes of stibines; early studies suggested fragmentation of the stibine or X/R exchange [7].…”

“…As is clear from [177], and this reference contains a thorough discussion of the various contributions to the observed chemical shifts. Solution NMR studies in chlorocarbon solvents also reveal that some [GaX 3 (ER 3 )] undergo fast ligand exchange in solution in non-coordinating solvents at room temperature or above (depending upon the specific combination of ER 3 /X present), and cooling the solutions may be necessary to observe resonances and spin-spin couplings [170,171,176]. In solution in chlorocarbon solvents, 31 [205].…”

“…[186]. there is no evidence for the formation of [GaX 2 {Et 2 P(CH 2 ) 2 PEt 2 }] + [170,176,180]. The diphosphinoalkene cis-Ph 2 PCH = CHPPh 2 reacts with GaX 3 (X = Br or I) in hot toluene to form [X 3 Ga(-transPh 2 PCH = CHPPh 2 )GaX 3 ], the cis → trans isomerisation being confirmed spectroscopically and by the X-ray structure of the bromide complex [181].…”