Amidine metal complexes

A. Amidinate and guanidinate complexes of main group metals 1. Group 1 metal complexes useful starting materials... 

These lithium derivatives were found to be excellent reagents for the introduction of the new amidinate scorpionate ligands into Group 4 metal complexes, and a series of neutral titanium and zirconium complexes were prepared according to Scheme 189 and fully characterized. 

Pinacolone, o-(diphenylphosphino)benzoyl-coordination chemistry, 401 Piperidine, IV-hydroxy-metal complexes, 797 pA a values azole ligands, 77 Plant roots amino acids, 962 carboxylic acids, 962 Plastocyanin copper binding site, 557 copper(II) complexes, 772 copper(II) site in, 770 Platinum, dichlorobis(benzonitrile)-IR spectrum, 264 Platinum, cis-dichlorodianunine-antitumor activity, 34, 979 Platinum, ethylenebis(triphenylphosphine)-reactions with 5,6-dimethyl-2,l,3-benzothiadiazole, 194 Platinum blue formation, 265 Platinum complexes acetylacetone reactions, 380 amides, 491 amidines... 

The reaction of a variety of liganded metal derivatives with carbodiimides give [1+2] or [2+2] cycloadducts or more complicated products resulting from rearrangement or reductive coupling reactions. Also, amidinate complexes, which are sometimes obtained in the reaction of metal complexes with carbodiimides, are included. 

The lithium amidinates are used as precursors for homoleptic lanthanide amidinates. Lanthanide amidinate complexes have a high catalytic activity in the polymerization of ethylene. They are also used in the manufacture of membranes. Lanthanide amidinate complexes 37 (La=Er, Y, Gd) are also obtained from alkyl metal complexes 36 and... 

The use of amidinato catalyst systems for the polymerization of olefins has first been reported in a patent application by us in cooperation with BASF company [6,7,46]. Since then various other patents dealing with the use of amidinato metal complexes as catalysts for olefin polymerizations have appeared. However, the main focus of these studies was on the use of group 4 metal amidinates as these have been found... 

An interesting organolanthanide-catalyzed reaction which has been studied in recent years is the addition of terminal alkynes to carbodiimides leading to the novel class of ,A -disubstituted propiolamidines. It was found that half-sandwich rare earth metal complexes bearing silylene-linked cyclopentadienyl-amido ligands can act as excellent catalysts in this addition reaction. As illustrated in Scheme 58, a rare earth amidinate species has been confirmed to be a true catalytic species [68]. 

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]... 

In addition to their thermodynamic propensity to dimerize [16], free acyclic car-benes containing alkyl groups are prone to decomposition via intramolecular C—H insertion reactions that lead to net elimination of an alkene (Scheme 16.3a) [35]. Loss of two alkene equivalents has been observed to occur from an Alder-type ADC bound to W or Mo tetracarbonyl fragments, resulting in conversion to an amidine ligand (Scheme 16.3b) [36]. This process appears to be limited to zerovalent metal complexes and may be facihtated by the unusual -(C,N) binding mode of the carbene. 

Traditionally, aluminum alkoxides have been used as homogeneous catalysts for the Tishchenko reaction. Other catalysts such as boric acid and a few transition-metal complexes have also been used. However, these catalysts are either reactive only imder extreme reaction conditions or very slow. Recently, great effort has been focused on the development of organolanthanide complexes as catalysts because of their high Lewis acidity, easily tunable coordination sphere around the metal, and environmentally friendly property. Series of organolanthanide complexes, such as alkyls, amides, and amidinates, were found to be highly efficient catalysts for the Tishchenko reaction. The proposed catalytic mechanism is provided in Scheme 11, and the precatalyst reacts with aldehyde to give lanthanide alkoxide as the catalytic active species. 

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