Insertion into phosphorus-hydrogen bonds

The reaction of phosphine (produced in situ from magnesium phosphide and hydrogen chloride in dioxan solution) with 1,5-diketones gives106 the phosphorina-none derivatives (104). Carbonyl compounds and heterocumulenes (e.g. CO2, CS2) insert into the germanium-phosphorus bond of germaphospholans to form derivatives of the germaphosphepin system [e.g. (105)].106>107... 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

H-[P], where [P] = PR2, P(0)R2, and P(0)(0R)2]. The reaction commences by insertion of Pd into the P—H bond, generating H-Pd-[P], which then undergoes insertion of the alkyne RCsCR either into the Pd-H or Pd-P bond, giving rise to RCH=C(R)Pd[P] or HPdC(R)=C(R)[P], respectively. The actual outcome depends on the geometrical arrangement of the phosphorus group and of the metal centre. Alkyne insertion into the metal-hydrogen (Pd or Ni) bond has been shown to occur with a considerably lower activation barrier than that into the metal-phosphoms bond. ° ... 

Different regioselectivity observed in Pd-catalyzed and Rh-catalyzed reaction originates from reaction mechanisms, which involve alkyne insertion into the metal-phosphorus bond in case of Pd (Scheme 8.7) and alkyne insertion into the metal-hydrogen bond in case of Rh (Scheme 8.9). In both cases stereoselectivity remains the same and the reactions proceeds as ryn-addition. In case of Rh-mediated transformation this results in selective formation of a single product with -configuration of the double bond. 

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