A remarkable switch from a diamination to a hydrohydrazination catalyst and observation of an unprecedented catalyst resting state.
A remarkable switch from a diamination to a hydrohydrazination catalyst and observation of an unprecedented catalyst resting state.
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DOI：
10.1002/anie.201206249
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发表时间：
2012-12
影响因子：
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通讯作者：
Andrew D. Schwarz;Chee S. Onn;P. Mountford
中科院分区：
文献类型：
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作者：
Andrew D. Schwarz;Chee S. Onn;P. Mountford
Group 4 imido complexes,(L) M= NR,[1] and, more recently, hydrazido complexes,(L) M= NNR2,[2] undergo a range of addition or insertion reactions of their M= N multiple bonds with many unsaturated and saturated substrates. This reactivity has led to a number of new bond-forming methodologies. In the case of hydrazides, reductive cleavage of the NαÀNβ bond can also occur with formally oxidizable substrates, such as CO,[2b] isocyanides,[2g, o] and alkynes,[2j, l, m] in the presence of suitably activating supporting ligand sets, such as bis (cyclopentadienyl) and diamide–amine types. We recently found [2l, m] that the hydrazide complex I (Scheme 1) and certain homologues react with terminal or internal alkynes to form metallacycles of the type II. In the case of I, these metallacycles cannot be isolated but proceed immediately at temperatures below 08C to form exclusively vinyl imides III. Furthermore, both I and III catalyze the 1, 2-diamination of terminal alkynes to form diaminoalkenes IV.[2l] This transformation is a new reaction of hydrazines with alkynes, which usually undergo hydrohydrazination, also via postulated metallacycles of the type II.[1e, 2c, d, 3] These metallacycles undergo protonolysis of the TiÀC and TiÀN bonds to form hydrazones V via transient mixed bis (hydrazido (1À)) intermediates VI. The more widely studied hydroamination reaction of alkynes, alkenes, and allenes with Group 4 metals [1c, e, 4] has been explored in a series of elegant mechanistic and computational [3b, 5] studies. Three mechanisms have been established: the “imide route”(the most common) through a [2+ 2] cycloaddition reaction of an M= NR bond,[3a, 6] the “amide route” through substrate migratory insertion into an MÀNRR’amide bond,[7] and a proton-assisted CÀN bondforming mechanism via an amide intermediate.[8] We have recently been developing further the chemistry of compounds of the type I and its homologues.[2m, o, 9] As part of this program we prepared the closely related compound [Ti (N2 iPrN)(NNPh2)(py)](1; N2 iPrN= MeN (CH2CH2NiPr) 2) containing sterically less demanding isopropyl substituents in the ligand periphery in place of the SiMe3 groups in I. Compound 1 was prepared in 72% yield from Li2N2 iPrN and [Ti (NNPh2) Cl2 (py) 3]. The solid-state structure [10](see the Supporting Information) establishes the trigonal-bipyramidal geometry shown in Scheme 2. This geometry is also predominantly maintained in solution according to NOE experiments. The hydrazide ligand in the solid-state structure of 1 occupies the electronically preferred [11] axial position trans to the NMe donor, whereas in I it lies exclusively in the equatorial position, which is the sterically preferred site. Minor resonances in the 1H NMR spectrum of 1 are attributed to the isomer with NNPh2 in the equatorial position. The treatment of 1 with HCCTol (1equiv; Tol= 4-C6H4Me) in C6D6 led to 50% conversion of 1 and complete conversion of the alkyne into a new compound, 2a. A second reaction with a 2: 1 ratio of the alkyne to 1 gave quantitative conversion into 2a, which was isolated in 91% yield when the reaction was scaled up and carried out in Et2O. Compound 2a is the unusual acetylide–vinylhydrazide (1À) compound [Ti-(N2 iPrN)(CCTol){N (NPh2) C (H) C (H) Tol}] illustrated in
