Imido ligands transition metal complexes with

The 1,2-addition of C—H bonds across metal-heteroatom bonds has been reported for two different classes of complexes early transition metal d° complexes with imido ligands and late transition metal complexes with amido, hydroxo, and aryloxo ligands (Scheme 11.36). These transformations are potentially related to o-bond metathesis reactions discussed above however, the presence of a lone pair on the heteroatom that receives the activated hydrogen may impart important differences. 

Reactions with Transition-Metal Compounds. The numerous pubhshed products of reactions of transition-metal compounds with a2iridines can be divided into complexes in which the a2iridine ring is intact, compounds formed by reaction of a2iridine with the ligands of a complex, and complexes in which the a2iridine molecule is fragmented (imido complexes). 

Bis-NHC CNC-type pincer ligands were first used with Pd and, later on, coordinated onto early-transition metal complexes. The titanium (III) complex 35 was readily prepared from (THF)3TiCl3 and the free bis(carbene)pyridine, whereas the imido Ti complex 36 was obtained from Ti(NtBu)Cl2(pyridine)3 (Scheme 14.19) [66,67]. The pincer complex 35 was tested in ethylene polymerization. With 500 equivalents of MAO cocatalyst, an activity of 791kgmor bar h was observed. 

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

Lu atom (Lu-N 2.352(4) A). The formation of the dianion complex apparently proceeds by nucleophilic addition of the imido unit to the C N group of benzoni-trile, which demonstrates that a lanthanide-imido bond, even in a bridging form, is very reactive. This is in contrast with what was observed previously for bonds between transition metals and bridging imido ligands, which are usually robust and unreactive. Moreover, the resultant product represented the first metal complex of an amidinate dianion, in contrast to the well-known complexes of various metals with amidinate monoanions [RNC(R0NR] as ligands [6,7]. The dianion complex and related complexes derived from imido lanthanide species react with excess of benzonitrile under selective formation of the cyclotrimerization product 2,4,6-triphenyl-1,3,5-triazine [72]... 

As noted above, the complexes of corroles with metals of the first transition series comprise the majority of reported metallocorroles. Many investigations have focused on the usual bioinorganic suspects, Cu and Fe. A number of computationally heavy reports on the electronic and molecular structures and spectroscopic properties of Cu corroles have been produced over the last few years, while the field has seen numerous attempts to formalize consensus electronic structural descriptions of Co and Fe corroles. There is also a rich literature describing the catalytic utility of high-valent Cr and Mn complexes with oxo, imido, or nitrido ligands, and a small amount of work has been performed on Ti and V corroles. Ni corroles have been reported in the literature as well, but investigations of their properties have often been folded into larger studies. 

In the ground state, the oxygen atom possesses two unpaired electrons (l-4a). It is therefore a ligand of X2 type, which can bind to a transition metal to form an 0x0 complex. The sulfido (S) and imido (N-R) (l-4a) ligands behave similarly. Atomic nitrogen, with three unpaired electrons, is an X3 ligand (l-4b), giving nitrido complexes. In each case, one therefore considers all the unpaired electrons on the atom bound to the metal. 

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