Organonitrile Ligands

The complexes containing organonitrile ligands themselves undergo a variety of reactions (Scheme 44). Whilst the structures of the five-coordinate cations remain a matter for speculation, the six-coordinate cation [Rh(NO)(MeCN)3(PPh3)2]2+ has been shown to have the structure (138) by X-ray crystallography.1343... 

Iron(II)-hydrido complexes containing organonitrile ligands of the form [FeH(L)(dpe)2] [dpe = l,2-bis(diphenylphosphino)ethane L = CHjCN, etc.] are reduced by the solvated electron in methanol the FeH(L)(dpe)j product rearranges, losing L to give the known FeH(dpe)2 complex (k = 10 - 10 s with CHj being fastest)" . ... 

Reaction of a similar organonitrile ligand with [Rh(/u-Cl)(COD)]2 led to a cw-rhodium complex, [RhCl(CO)2(nOCB)], which was found to be mesomorphic over one degree only (Cr 78 N 79 dec.) above which it decomposed. 

Coordination compounds with organonitrile ligands are of considerable interest due to the increased susceptibility of the coordinated nitrile to nucleophilic attack by reagents such as hydroxide ion. Rate accelerations of 10 in base hydrolysis (nitrile-> amide) have been observed. Two new aromatic organonitrile complexes of [Co(NH3)5] with 2- and 4-nitroben-zonitrile have been prepared, and their base hydrolysis to coordinated carboxamides studied. The second-order rate constants for base hydrolysis are 180 4 and 510 90 M s at 25°C and / = 1.0 M for the ortho and para isomers, respectively. Rate constants for the hydrolysis of 11 coordinated aromatic nitriles follow a Hammett-type correlation with log koH = l-93o- + 1.30 at 25 C and / = 1.0 M. Carbon-13 NMR studies of the free and coordinated nitriles indicate similar chemical shifts, so that the variation in the slope of the Hammett plots for free- and coordinated-nitrile hydrolysis is a transition-state effect rather than a ground-state phenomenon. 

Tab. 4 Values of the Pl ligand parameter for organonitriles (N=CR) at metal centers Ms with a different electron-richness (Es) [24]...

Organonitriles are usually taken as weak c-donors and n-acceptors (contrasting in that aspect the isoelectronic CO and explaining the lability of the complexes), but recent LCAO-MO calculations6 indicate a potential a-donor character in MeCN. Relevant orbital energies for this ligand are shown in Figure 1. 

The interactions of compounds containing the oxime group with coordinated organonitriles are very important in template syntheses [384,413-416], These reactions take place as a nucleophilic addition and lead to the formation of complexes with unusual iminoacyl ligands. The iminoacylation reaction was studied in detail for various oximes and organonitriles, coordinated to PtCl4 [384,413-416]. Thus, the template transformation (3.192) of the discussed type in case of the oximes 744 takes place in acetonitrile or chloroform and yields complexes of the type 745 [413a] ... 

Both mono and dinitrosyl cations may be prepared. Salts of the tetrahedral dinitrosyl cation can be prepared either from rhodium nitrosyls (equation 56) or by addition of nitric oxide to ionic rhodium(I) complexes (equation 57). Both nitrosyl groups in complex (47) are bent. The action of dppe upon the i)A(triphenylphosphine) complex produces N2O. Penta- and hexacoordinate mononitrosyl cations are more common and are usually prepared by the action of NOPFe or NOBF4 on rhodium(I) complexes in organonitrile solvents (equation 58). The principal reactions of the complexes are substitutions of the nitrile ligands (equations 59-61). A noteworthy feature of (48), [Rh(NO)(MeCN)3(PPh3)2]+, is that the MeCN ligand trans to the bent nitrosyl group is said to be bent. 

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