201869-74-1Relevant academic research and scientific papers
The carbenoid nature of halophosphines. Carbene-like insertion mechanism in the reaction of chlorophosphines with Cp2NbH3
Nikonov, Georgii I.,Grishin, Yuri K.,Lemenovskii, Dmitry A.,Kazennova, Nadezhda B.,Kuzmina, Lyudmila G.,Howard, Judith A. K.
, p. 183 - 198 (1997)
We have studied the reactivity of Cp2NbH3 (1) with different chlorophosphines and showed that all the reactions occur at the niobium-hydride bond and proceed by two competitive routes, via the direct insertion of a chlorophosphine into the Nb-H bond and electron or/and hydride transfer mechanism. Reaction of 1 with the unhindered dialkyl-and diaryl-chlorophosphines C1PR2 (R = Et, Bu, Pri, Ph) gave the insertion product - the ionic complexes [Cp2NbH2(PHR2)]C1 (2) - in high yields. In contrast, reaction of 1 with the bulkier C1PBu12 proceeded much slower and resulted in the steady formation of Cp2NbC12 and HPBu12. Cp2NbC12 was also the product of the reactions of 1 with excess of C1P(OEt)2 and catecholechlorophosphite 7. The reaction of 1 with one equivalent of cyclic chlorodiaminophosphine C1P(N(CH3)2CH2-)2 (5) resulted in two competitive routes that led to the ionic complex [Cp2NbH2(HP(NR2)2)]C1 (2f) and molecular complex Cp2NbC1(HP(NR2)2) (6j). The reaction of 1 with two equivalents of cyclic 1-chloro-5,5-dimethyl-1-phospha-2,6-dioxahexane gave cationic diphosphite complex [Cp2Nb(PHR2)2]C1 (8) in high yield. This reactivity was explained in terms of the carbenoid nature of halophosphines due to the proposed relationship in the electronic structures of halophosphines and singlet methylene. Thus, reaction of 1 with the unhindered dialkyl-and diaryl-chlorophosphines proceeded by the direct insertion of a chlorophosphine C1PR2 into the Nb-H bond whereas with the more electron withdrawing substituents R at phosphorus the electron or/and hydride transfer mechanisms, leading to 6 and eventually to Cp2NbC12, could be operative. This concept also allowed us to explain the reactivity of chlorophosphines toward different unsaturated organic products. The facile syntheses of complexes Cp2Nb(PHR2)C1 (6) and Cp2Nb(PHR2)H (11) by the thermolysis and deprotonation of 2, respectively, was performed and the comparison with other methods was undertaken. Crystallographic studies of complexes 8 and Cp2Nb(PHPri2)Br are reported.
