All-Organometallic Analogues of Zeise's Salt for the Three Group 10 Metals

Ethene has been found to be able to split the electron-deficient pentafluorophenyl bridging system in [NBu 4 ] 2 [{M(C 6 F 5 ) 2 }(μ-C 6 F 5 ) 2 ] to give the corresponding mononuclear compounds [NBu 4 ][M(C 6 F 5 ) 3 (η 2 -C 2 H 4 )] (M = Pt ( 1 ), Pd ( 2 )) in reasonable yield. Compounds 1 and 2 are well-behaved species and have been isolated and characterized by analytical and spectroscopic methods. The crystal structure of 2, as established by X-ray diffraction methods, reveals that the Pd atom is in an approximately SP -4 environment defined by the ipso -C atoms of the three σ-bound C 6 F 5 groups (C 6 F 5 -κ 1 ) and the midpoint between the doubly bonded C atoms of the metal π-bound ethene molecule (η 2 -C 2 H 4 ). The ethene molecule is coordinated upright, and the C C bond length (133.6(6) pm) is the same as in the free ligand (133.7(2) pm). The nickel homologue [NBu 4 ][Ni(C 6 F 5 ) 3 (η 2 -C 2 H 4 )] ( 3 ), formed by the low-temperature reaction of [NBu 4 ] 2 [Ni(C 6 F 5 ) 4 ] with B(C 6 F 5 ) 3 in the presence of C 2 H 4, could not be isolated but only spectroscopically detected in solution. The experimentally established stability of the [M(C 6 F 5 ) 3 (η 2 -C 2 H 4 )] - species has been found to follow the trend calculated by DFT methods for the M-(η 2 -C 2 H 4 ) bond strength: Pt > Pd > Ni. Furthermore, quantitative estimates of back-bonding in the [M(C 6 F 5 ) 3 (η 2 -C 2 H 4 )] - and [MCl 3 (η 2 -C 2 H 4 )] - anions were obtained using NBO analyses of electron populations of the relevant donor−acceptor orbitals and the second-order stabilization energy associated with the charge transfer (CT) interactions describing the back-bonding phenomenon.