Organometallics square-planar structures

Following the aforementioned pioneering work, many other organometallic complexes of nickel(II) were prepared using different synthetic procedures. Complexes containing one molecule of tertiary phosphine were prepared using methods similar to that reported in equations (142) and (143) and Scheme 13.1193-11951219-1223 All of these diamagnetic compounds have the square planar structure exemplified by (155).1193... 

The formation of five-coordinate gold(III) has been demonstrated clearly in the complexes of 2,9-dimethyl-l,10-phenanthroline and 2,2 -biquinoline, which have the distorted square pyramidal structures (91) and (92). However, the structures of the ligands prevent square planar coordination, so that these examples are atypical.613-615 However, a related organometallic derivative, [AuCl(C4Ph4)(phen)], is known and has a similar distorted square pyramidal structure.616... 

Chemistry is stereochemistry. After development of the fundamental synthetic methods and the structural characterization of many important compounds in such an expanding field as organometallic chemistry during the past 25 years, the problems demanding solution become more subtle, so that more elaborate techniques, e.g., kinetic and spectroscopic measurements, as well as stereochemical methods, gain in importance. Stereochemical information can be obtained by a variety of techniques. Hence, the study of such stereochemical aspects as cis-trans isomerism in square-planar and octahedral transition-metal compounds was a consequence of the increasing availability of IR spectrometers, and temperature-dependent NMR spectroscopy proved to be an extremely valuable technique for the study of nonrigid systems. 

Aside from full catalytic cycles, or reaction steps within them, as discussed above, structural issues about organometallic complexes with catalytic properties have also been analyzed with QM/MM methods. For instance, Helmchen and coworkers carried out a conformational analysis of two (w-l,3-dimethylallyl)(phosphinooxazoline)Pd complexes [128], and Magistrato et al investigated the role of n-n stacking interactions in square planar palladium complexes [129]. 

The silver ion is situated exactly in the center of the cavity as an X-ray crystal structure demonstrates. Therefore 31 is the first square-planar d °-organometallic complex. Besides, carbon-silver couplings in the C-N MR spectrum prove that the nature of the complex is static, i.e. the central ion is bound tightly to the ligand 30. 

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