N-Acid ligand

Low oxidation state complexes are usually stabilised by n-acid ligands such as CO, PR3 (phosphines), olefins etc. The use of the word acid here refers to Lewis acidity, i.e. electron acceptance. Binding to n acid ligands occurs in a synergic fashion that comprises two components ... 

Carbonyl and alkene complexes of ruthenium have been previously reviewed. The syntheses of [Ru(CO)(NH3)5]2+ are summarized in Scheme 3. The dependence of vc=0 upon counterion and upon solvent has been discussed. 88 The Mossbauer spectrum of [Ru(CO)(NH3)5 2+ has been reported.27 120 The replacement of HzO by isn in /razw-[Ru(L)(NH3)4(OH2)]2+ has been assessed, the lability increasing in the order L = CO = N2 < isn < py < imid (N bound) az NH3 < OH- < CN-< SO2- < imid (C bound).189 For n acid ligands good correlation between specific rate and k-l/2 values for the ruthenium(II)/(III) couple was observed.189... 

Stable rhodium(I) complexes usually require the presence of at least one jr-acid ligand. The presence of bnlky n-acid ligands tends to lead to coordinative unsaturation by ligand dissociation, which can enhance the catalytic activity. Tertiary phosphines meet both these requirements and have the added advantage of conferring solubility in organic solvents. 

Compounds with n-acid ligands, (a) Binary carbonyls are formed by all but Pd and Pt (page 690), the majority of them polynuclear. Substituted polynuclear carbonyls are known for Pd and Pt, and all six elements give carbonyl halides and a wide variety of carbonyl complexes containing other ligands. 

Most complex chemistry of the actinides is in aqueous solution. However, a number of neutral complexes and complexes between halides and neutral donor ligands such as Ph3PO or Me2SO are known. There are very few complexes formed by n acid ligands, providing a notable contrast to the J-block elements for example, there is no evidence for the bonding of NO or alkenes. However, uranium carbonyls have been trapped in matrixes at4°K.16a... 

The bonding between the transition metal and the group 13 element has been studied extensively by computational methods. Because RM compounds have a valence electronic structure consisting of a filled orbital of a symmetry and two unfilled orbitals of n symmetry, they are analogous to carbonyl ligands in that they can act as sigma donors and pi acceptors see n-Acid Ligand). Such an electronic structure... 

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