Selectivity of the metalation reaction

There are several reports of metalation reactions with phosphines having more than one site for C-H activation. Thus, the reaction of rhodium acetate and the phosphines P(o-XC6H4)Ph2, (X = Cl, Br), initially produced only compounds metalated at the unsubstituted phenyl rings. The crystal structure of the bimetalated compound with P(m-CH3C6H4)3 confirmed that the metalation occurs selectively at the carbon atom trans to the methyl group.  

There are two examples reported of rhodium(II) compounds metalated at an alkyl group of a phosphine.One compound with the formula Rh2(//2-02CCH3)2[/ 2 (CH2)PPh2][/ 2-(C6H4)PPh2]PPh3 (18) was obtained by seren- 

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