Formation of the donor-acceptor complexes of group 13 metal derivatives with nitriles and isonitriles X3M-D (M = Al,Ga, In; X = H,Cl,CH3; D = RCN, FINC; R = H,CH3) and their subsequent reactions have been theoretically studied at the B3LYP/pVDZ level of theory. Although complexation with MX3 stabilizes the isocyanide due to the stronger M-C donor-acceptor bond, this stabilization (20 W mol(-1) at most) is not sufficient to make the isocyanide form more favorable. Relationships between the dissociation enthalpy DeltaHdegrees(298)(diss), charge-transfer q(CT), donor-acceptor bond energy E-DA, and the shift of the vibrational stretching mode of the CN group upon coordination Deltaomega(CN) have been examined. For a given metal center, there is a good correlation between the energy of the donor-acceptor bond and the degree of a charge transfer. Prediction of the DeltaHdegrees(298)diss on the basis of the shift of CN stretching mode is possible within limited series of cyanide complexes (for the fixed M,R); in contrast, complexes of the isocyanides exhibit very poor Deltaomega(CN) - DeltaHdegrees(298)(diss) correlation. Subsequent X ligand transfer and FIX elimination reactions yielding monomeric (including donor-acceptor stabilized) and variety of oligomeric cage and ring compounds with [MN](n), [MC](n), [MNC](n) cores have been considered and corresponding to thermodynamic characteristics have been obtained for the first time. Monomeric aluminum isocyanides X(2)AINC are more stable compared to AI-C bonded isomers; for gallium and indium situation is reversed, in qualitative agreement with Pearson's HSAB concept. Substitution of X by CN in MX3 increases the dissociation enthalpy of the MX2CN-NH3 complex compared to that for MX3-NH3, irrespective of the substituent X. Mechanisms of the initial reaction of the X transfer have been studied for the case X = R = H. The process of hydrogen transfer from the metal to the carbon atom in H3M-CNH is thermodynamically favorable and is likely to be intramolecular. By contrast, intramolecular hydrogen transfer in H3M-NCH has been definitely ruled out. Head-to-tail dimeric species [H3M-(NC)H](2) are formed exothermically and exhibit low H...H distances, which can assist in hydrogen transfer, and are likely to be the starting point for H-2 elimination. Elimination of H-2, CH4, and C2H6 from X3M (NC)R adducts is very favorable thermodynamically; by contrast, elimination of HCl and CH3Cl is highly unfavorable even if formation of oligomer species takes place. Thus, high-temperature generation of gas-phase rings and clusters has been predicted viable in the cases X = H,CH3 and their presence in the reactor media should not be neglected. Moderate stability of [HMCH2NH](4) clusters (especially in the cases M = Ga, In) makes these species viable intermediates of gas-phase reactions. Their formation may be responsible for the carbon contamination in the course of metal organic chemical vapor deposition processes of group 13 binary nitrides.