Phosphines, tris adducts

The sterically demanding phosphine tris(trimethylsilyl)phosphine, P(SiMe3)3, proved to be very important in the development of the chemistry of the Al-P bond. A number of aluminum-phosphorus adducts were reported in the last decade. In particular, Cl3Al-P(SiMe3)3 toluene and Br3APP(SiMe3)3 toluene, with Al-P bond distances of 2.392(4) A and 2.391(6) A, respectively, were reported. These virtually identical Al-P bond distances are extremely short. The aluminum atoms in both complexes may be described as four-coordinate tetrahedral. 

Electron donors which interact at only one end of the X2 or XY molecule form simple adducts (Fig. 1, mode A), often referred to as a spoke structure. The diiodine complex of tris(diethylamino)phosphine selenide (PAQKIB) [ 135] shown in Fig. 2a is an excellent example of this mode, as the Se- I distance at one end of the I2 molecule is 2.715 A, while at the other end there are no close contacts with any other atom. 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

To date, however, only few reactions between phosphine and a non-metal halide, in which a chemical bond is formed between phosphorus and a non-metal by HCl condensation, are known. To these, apart from the above-mentioned reactions, belongs also the reaction with CF3SCI which, depending upon the chosen proportions of the reactants, in a sealed tube at -95 °C leads to the formation of (CF3S)2PH or (CF3S)3P Both compounds are not very stable thermally and decompose at 40-50 °C. Tris(trifluoromethylthio)-phosphine forms an unstable adduct with chlorine, which decomposes at 0 °C to give a mixture of PCI3, bis(trifluoromethyl)-disulphide and trifluoromethyl-sulphenyl chloride. 

Tripiperidino-, tripyrrolidino-, trimorpholino-, tri(methylamino)- and tri(cyclohexylamino)-phosphine sulfides forms adducts with Snw halides with a lowering of v(P—S) of 45 cm-1. The first two ligands form 1 2 adducts with PdCl2 and both 1 1 and 1 2 adducts with CdX2 (X = Br, I).102... 

The radical reductive cyclisation of diesters to acyloins (see also Section 5.9.1, p. 628) is an important method of synthesis for ring sizes from four-membered upwards. The example selected here is 2-hydroxy-3-methylcyclopent-2-enone ( corylone ) (29) (Expt 7.10), which is an important perfumery and flavouring material.53 In the first step (i), methyl acrylate is converted into its dimer with tris(cyclohexyl)phosphine in pyridine solution.5b Step (ii) is the protection of the double bond by conversion into the dimethylamino adduct. The acyloin reaction is step (iii), and the product is trapped as its bis(trimethylsilyl)ether. Finally, in step (iv), the protecting dimethylamino and trimethylsilyl groups are removed by passage down a column of silica gel. 

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