Carbon monoxide isoelectronic analogs

Based on this concept, Whitby and co-workers [110] reported an interesting palladium-catalyzed three-component synthesis of aromatic and heteroaromatic amidines 133 starting from unsaturated halides, amines, and t-butylisocyanide (Scheme 8.53). The catalytic cycle for this iminocarbonylative coupling reaction is analogous to the reactions incorporating carbon monoxide-isoelectronic with isocyanides-as the third partner [111]. 

K2[Fe(NO)2(CN)2]. My former co-worker R. Nast (83) showed that the reaction of carbon monoxide with K4[Ni2I(CN)6] and K4[Ni°(CN)4] in liquid ammonia gave nickel cyanocarbonyl complexes with monovalent and zero-valent metal atoms. The isoelectronic hexacyanoiron(III) or tetra-cyanonickel(II) complexes correspond to the cyanocarbonyls [Feu(CN)5 CO]3-, [Ni (CN)3CO]2-, or [Ni°(CN)2(CO)2]2-. Cobalt is analogous to nickel in forming the complex [Co(CN)3CO]2-. According to our earlier work, [Fe"(CN)5CO]3- and [Fem(CN)6]3- are isosteric (87). Other structural investigations were concerned with tetracyano and tetracarbonyl complexes (88). 

There are numerous theoretical and experimental results demonstrating that simple molecular solids transform into nonmolecular phases at high pressures and temperatures, ranging from monatomic molecular solids such as sulfur [61], phosphorous [62] and carbon [63] to diatomic molecular solids such as nitrogen [8, 9,40], carbon monoxide [12] and iodine [20, 21], to triatomic molecules such as ice [24, 25], carbon dioxide [10, 31, 37] and carbon disulfide [64, 65] to polyatomics such as methane [27, 28] and cyanogen [11], and aromatic compounds [29]. In this section, we will limit our discussion within a few molecular triatomics first to review the transformations in two isoelectronic linear triatomics, carbon dioxide and nitrous dioxide, and then to discuss their periodic analogies to carbon disulfide and silicone dioxide. 

A majority of the nitrosyl complexes contain NO (nitrosyl or nitrosonium ion) as the hgand. The nitrosyl cation is isoelectronic with carbon monoxide. Hence, the bonding between nitrogen and metal in nitrosyls is analogous to that of carbon and metal in carbonyls. However, the hgand nitrosyl (NO ) is a three-electron donor, as it donates one electron to the metal ion prior to the donation of an electron pair for the formation of a coordinate covalent bond. 

Examples of complexes in this class are given in Table 25. The taUe shows that these complexes are closely related to the corresponding complex cyanides, in their occurrence, colour and magnetic properties. This close analogy arises since the cyanide and acetylide anions are iso-electronic and presumably bond to the metal in a similar manner. Both ligands would be expected to have acceptor properties as does the neutral carbon monoxide molecule, which is also isoelectronic. The bonding in the systems M—C X, where X = O, N or CR, may be represented as shown in Figure 67. 

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