Cationic, Methylene-Bridged, Intramolecular Donor-Acceptor Systems Based on Zirconium and Hafnium and Phosphino-methanides

Abstract

A new access to cationic zirconium and hafnium compounds [L 2 MCH 2 PR 2 ][MeB(C 6 F 5 ) 3 ] (L = Cp, Ind; R = iso-Pr, tert-Bu; M = Zr, Hf) exhibiting an intramolecular donor-acceptor system was established by treating the precursors L 2 M(Me)CH 2 PR 2 with B(C 6 F 5 ) 3 (BCF). Precursors 1-6 [L 2 M(Me)CH 2 PR 2 with L = Cp, Ind; R = iso-Pr, tert-Bu; M = Zr, Hf] were fully characterized. The crystal structures of these compounds revealed large M-CH 2 -P bond angles * Prof. Dr. N. W. Mitzel 909with values of about 134°indicating the absence of interactions between the Lewis-acid and Lewis-base. The cationic compounds [L 2 MCH 2 PR 2 ][MeB(C 6 F 5 ) 3 ] (7-12) were obtained by treatment of 1-6 with BCF. They were characterized by NMR spectroscopy, mass spectrometry, and elemental analyses; in H/D-scrambling experiments with H 2 /D 2 mixtures 7-12 disclosed their reactivity towards cleavage of hydrogen.intramolecular Lewis pair geminally bonded to the central metal atom. Journal of Inorganic and General ChemistryZeitschrift für anorganische und allgemeine Chemie ARTICLEIn the NMR spectra the anticipated patterns of resonances could be observed. The 13 C NMR chemical shifts of the methylene group of the tert-butyl compounds 2, 4, and 6 are found between δ = 49.7 and 52.3 ppm, the corresponding 1 H NMR chemical shifts between δ = -0.73 ppm and 0.05 ppm. The 31 P NMR spectra of compounds 2, 4 and 6 show singlets with a strong low-field shift in the range between δ = 50.8 and 51.6 ppm. The corresponding NMR spectroscopic data for the iso-propyl-substituted compounds 1, 3 and 5 show 13 C NMR shifts between δ = 43.2 and 48.7 ppm and 1 H NMR shifts between -0.55 and 0.15 ppm. However, the 31 P NMR chemical shifts of 1, 3 and 5 are found between δ = 19.5 and 21.1 ppm, i.e. in a completely different range and high-field shifted compared to those of compounds 2, 4 and 6.Crystalline samples of compounds 1-6 were obtained upon cooling either n-hexane, n-pentane, or toluene solutions to -30°C. The compounds crystallize in the monoclinic space groups P2 1 /n (1, 3, 5, 6), P2 1 /c (2) as well as P2 1 (4), respectively. Figure 1 exemplarily depicts the molecular structures of 1 and 3.