Novel bis(phosphine) pincer complexes of iridium based on ferrocene and ruthenocene have been synthesized. The reaction of 1,3-bis((di-tert-butylphosphino)methyl)metallocenes [t-BuP,CH,PM] (M = Fe, 10; M = Ru, 13) with [Ir(COE)2Cl]2 in refluxing toluene leads to the corresponding chloro-hydrido pincer complexes as a mixture of H-endo- (M = Fe, 11; M = Ru, 14) and H-exo-IrH(Cl)[t-BuP,C,PM] (M = Fe, 12; M = Ru, 15) isomers. Treatment of compounds 11, 12 and 14, 15 with NaH in hot cyclooctane generates corresponding dihydrido complexes IrH2[t-BuP,C,PM] (M = Fe, 6; M = Ru, 7). Reactivity of the chelated iridium atom in hydrido-iridium pincer complexes and oxidation centered at the iron atom of ferrocene-based pincer complexes were studied. Complexes H-exo-IrH(Cl)(CO)[t-BuP,C,PFe] (20), Ir(CO)[t-BuP,C,PFe] (21), and Ir(CO)[2,6-(tBu2PO)2C6H3] (30) were characterized by X-ray crystallography. On the basis of νCO values for carbonyl iridium derivatives, electronic characteristics of the corresponding fragments {Ir[t-BuP,C,PM]} n (n = 0, +1) were elucidated. Complexes 6 and 7 reveal unprecedented catalytic activity in cyclooctane dehydrogenation in the presence of tert-butylethylene as a hydrogen acceptor:  turnover numbers 3300, 2571, and 1843 were obtained for 6, 7, and the known complex IrH2[2,6-(tBu2PO)2C6H3] (4c), respectively, at 180 °C for 8 h. The high catalytic activity for 6 and 7 and the difference in the catalytic activity of these “isostructural” complexes are discussed in terms of steric and electronic effects.

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Palladium P,C,P pincer complexes based on ferrocene were synthesized for the first time. The reaction of 1,3-bis(dialkylphosphinomethyl)ferrocenes {1,3-(R2PCH2)2C5H3}Fe(C5H5) (2a, R=Pr i ; 2b, R=Bu t ) with PdCl2(NCPh)2 in refluxing 2methoxyethanol leads to the corresponding pincer complexes PdCl[{2,5-(R2PCH2)2C5H2}Fe(C5H5)] (3a, 3b). Ferrocene-based binuclear compound 3b reacts with [Cp2Fe]PF6 to form the ferrocenium-based pincer complex {PdCl[{2,5-(Bu t 2PCH2)2C5H2}Fe(C5H5)]}PF6 (4b), and this is the first example of ferrocene-based phosphine chelate oxidation centered on the iron atom. Treatment of complexes 3a and 3b with NaBH4 in refluxing ethanol leads to the complexes Pd(BH4)[{2.5-(R2PCH2)2C5H2}Fe(C5H5)] (5a, R=Pr i ; 5b, R=Bu t ), containing a BH4  group coordinated to the metal in the rarely occurring unidentate mode. The structures of 3a, 3b, and 5b were confirmed by X-ray analyses. Cyclic voltammetric investigations of complexes 2a, 2b, 3a, and 3b are also reported. The structural and spectroscopic features of the palladium ferrocene-based pincer complexes are discussed and compared with those of related compounds.