Iodination of α-Phosphino Enolate Complexes of Palladium(II) and Platinum(II). Synthesis and Crystal Structures of [(dmba)Pd{Ph2PC(I) C( O)Ph}] and of the Dipalladium(II) Complex [(dmba)Pd{Ph2PC C( O)Ph}Pd(I)(tmeda)] Obtained by Palladium(0) Insertion into the Carbon−Iodine Bond

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Abstract
Electrophilic attack of 1 equiv of I2 on a PCsp2 carbon of the Pt(II) complex (1) afforded (2) in 90% yield. Complex 2 was subsequently deprotonated by NaOEt in ethanol to give the bis(enolato) complex (3). This α-phosphino, α-iodo enolato complex was obtained directly and quantitatively by the reaction of 1 with 1 equiv of N-iodosuccinimide (NIS). When 2 equiv of NIS was used, the symmetrical complex (4) was formed selectively. In contrast to I2, NIS was also able to functionalize the phosphino enolate ligand of complexes to give the corresponding iodo derivatives (C N = dmba (5) or 8-mq (6)). These represent the first examples in which a phosphino enolate C−H bond has been directly functionalized, i.e. replaced by a C−X bond. Attempts to use this procedure with or with were unsuccessful. Reaction of 5 with Pd(dba)2 in the presence of tetramethylenediamine (tmeda) or 2,2‘-bipyridine (bipy) afforded (7) and (8), respectively. The solid state structures of complexes 5 and 7·CH2Cl2 have been determined by single-crystal X-ray diffraction: 5 crystallizes in the monoclinic space group P21/n with Z = 4 in a unit cell of dimensions a = 12.867(3) Å, b = 10.625(3) Å, c = 19.509(6) Å, and β = 102.23(2)°; 7·CH2Cl2 crystallizes in the monoclinic space group C2/c with Z = 8 in a unit cell of dimensions a = 35.906(3) Å, b = 13.565(3) Å, c = 15.775(2) Å, and β = 95.099(10)°. Complex 7 contains two palladium(II) centers, in a square-planar environment, connected by the P−C unit of a phosphino enolate ligand which adopts an unprecedented μ-η2(P,C):η2(P,O) bonding mode. The two coordination planes are almost orthogonal and make a dihedral angle of 88.0(2)°, which minimizes the steric hindrance between the ligands.

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