From Dinuclear Zirconium(+3)‐Phosphido Complexes {[Cp2ZrP(H)R]2} to the First Neutral Zirconocene–Phosphinidene Dimers [(Cp2ZrPR)2] by P–H Dehydrogenation

Abstract

AbstractThe syntheses and structures of the new zirconium(+3) silylphosphanido complexes {[Cp2ZrP(H)R]2} 1a {Cp = η5‐C5H5; R = SiMe2C(iPr)Me2}, 1b (R = SiiPr3), and 1c (R = SiF(tBu)(2,4,6‐iPr3C6H2) are reported. The latter are easily accessible by the reaction of the lithium salts of the corresponding primary silylphosphanes with the Schwartz reagent [Cp2Zr(H)Cl] in THF at –70 °C. They can be isolated in the form of diamagnetic red‐black crystals in 68–85 % yield. The central structural motif of the complexes consists of planar (1a, 1b) and slightly puckered Zr2P2 rings (1c), and contains two d1‐Zr(+3) centers, which are antiferromagnetically coupled (super exchange, through‐bond interaction) although the transannular Zr–Zr separation is around 360 pm. Thus, the compounds have a biradicaloid electronic structure. Heating of solutions of 1a–c in toluene in the presence of Pd/C or [(Ph3P)2Pt(C2H4)] results in catalytic dehydrogenation of the P–H bonds, affording the first neutral zirconocene–phosphinidene dimers [Cp2ZrPR]23a–c in the form of deep red crystals in 72–88 % yield. The composition of the products is proven by multinuclear NMR spectroscopy, mass spectrometry and correct C,H‐combustion analyses. The molecular structures of 3a and 3c were additionally confirmed by X‐ray crystal structure analyses, showing that they consist of Zr2P2 rings with significantly shorter Zr–P distances than those observed in 1a and 1c. Interestingly, the dehydrogenation of the mostly sterically crowded derivative 1c occurs also in boiling toluene solutions without using a catalyst, but the process is prevented in a H2 atmosphere. This suggests that the Zr(+3) centers in 1c can serve as active sites for the P–H bonding activation, which, however, are deactivated in the presence of H2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)