Ammonia Activation by mu(3)-Alkylidyne Fragments Supported on a Titanium Molecular Oxide Model

作者：Aguado Ullate Sonia; Carbo Jorge J^*; Gonzalez del Moral Octavio; Martin Avelino; Mena Miguel; Poblet Josep M; Santamaria Cristina

来源：Inorganic Chemistry, 2011, 50(13): 6269-6279.

DOI：10.1021/ic2006327

Ammonolysis of the mu(3)-alkylidyne derivatives [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu(3)-CR)] [R = H (1), Me (2)] produces a trinuclear oxonitride species, [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu(3)-N)] (3), via methane or ethane elimination, respectively. During the course of the reaction, the intermediates amido mu-alkylidene [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu-CHR)(NH2)] [(R = H (4), Me (5)] and mu-imido ethyl species [{Ti(eta(5)-C5Me5)(mu-O)}(3) (mu-NH)Et] (6) were characterized and/or isolated. This achievement constitutes an example of characterization of the three steps of successive activation of N-H bonds in ammonia within the same transition-metal molecular system. The N-H sigma-bond activation of ammonia by the mu(3)-alkylidyne titanium species has been theoretically investigated by DFT method on [{Ti(eta(5)-C5H5)(mu-O)}(3) (mu(3)-CH)] model complex. The calculations complement the, characterization of the intermediates, showing the multiple bond character of the terminal amido and the bridging nature of imido ligand. They also indicate that the sequential ammonia N-H bonds activation process goes successively downhill in energy and occurs via direct hydron transfer to the alkylidyne group on organometallic oxides 1 and 2. The mechanism can be divided into three stages: (i) coordination of ammonia to a titanium center, in a trans disposition with respect to the alkylidyne group, and then the isomerization to adopt the cis arrangement, allowing the direct hydron migration to the mu(3)-alkylidyne group to yield the amido mu-alkylidene complexes 4 and 5, (ii) hydron migration from the amido moiety to the alkylidene group, and finally (iii) hydron migration from the mu-imido complex to the alkyl group to afford the oxo mu(3)-nitrido titanium complex 3 with alkane elimination.

• 出版日期2011-7-4