Insight into the Reaction of a Dinuclear Phosphinidene Complex with Nitriles

The phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 ; Cp*=C₅Me₅) reacted with malononitrile to give the 1,2‐dihydro‐1,3,2‐diazaphosphinine derivative 2 . The reaction of 1 with 1,4‐benzodinitrile gave [1,4‐{{W(CO)₅}₂P‐N=C(Cp*)}₂(C₆H₄)] ( 3 ), the first example of a cumulene‐like aminophosphinidene complex. The reaction of 1 with aniline gave the aminophosphinidene complex [(Ph)N(H)P{W(CO)₅}₂] ( 4 ). To compare the reactivity of benzonitrile and aniline with 1 , the phosphinidene complex 1 was reacted with three different isomers of aminobenzonitrile (2‐, 3‐, and 4‐aminobenzonitrile). These reactions gave an insight into the reaction pathway of 1 with benzonitrile derivatives. Compounds 5 , 6 a , 6 b , and 7 , which are derivatives of 1,2‐dihydro‐1,3,2‐diazaphosphinine or benzo‐2H‐1,2‐azaphospholes, were, as well as all other products, characterized by mass spectrometry, NMR and IR spectroscopy, and X‐ray structure analysis.     

Experimental and theoretical study on the reactivity of phosphorus-containing cubane type clusters [RMPR’]<Subscript>4</Subscript> (M = Ga,In) toward pyridine

Reactions of cubane type clusters [EtGaPSi(Me)₂Thex]₄ [Thex = CMe₂(Pr-i)] and {EtInP[Si(i-Bu)₃]}₄ with pyridine were studied. The temperature dependences of vapor pressure over individual solid compounds were measured using a membrane pressure gauge. At a temperature above 200°C the examined clusters undergo irreversible thermal decomposition due to instability of organic substituents. According to the experimental data, the cubane clusters do not react with gaseous pyridine below their decomposition temperature. Thermodynamic parameters for the isomerization of model clusters [HMPH]₄ (M = Ga, In) and their gas-phase reactions with pyridine were calculated by quantum-chemical methods. The addition of pyridine is thermodynamically allowed only at low temperatures.     

Fascinating transformations of donor-acceptor complexes of group 13 metal (Al,Ga, In) derivatives with nitriles and isonitriles: from monomeric cyanides to rings and cages

Formation of the donor-acceptor complexes of group 13 metal derivatives with nitriles and isonitriles X(3)M-D (M = Al,Ga,In; X = H,Cl,CH(3); D = RCN, RNC; R = H,CH(3)) and their subsequent reactions have been theoretically studied at the B3LYP/pVDZ level of theory. Although complexation with MX(3) stabilizes the isocyanide due to the stronger M-C donor-acceptor bond, this stabilization (20 kJ mol(-1) at most) is not sufficient to make the isocyanide form more favorable. Relationships between the dissociation enthalpy DeltaH degrees (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 DeltaH degrees (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) - DeltaH degrees (298)(diss) correlation. Subsequent X ligand transfer and RX 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)AlNC are more stable compared to Al-C bonded isomers; for gallium and indium situation is reversed, in qualitative agreement with Pearson's HSAB concept. Substitution of X by CN in MX(3) increases the dissociation enthalpy of the MX(2)CN-NH(3) complex compared to that for MX(3)-NH(3), 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 H(3)M-CNH is thermodynamically favorable and is likely to be intramolecular. By contrast, intramolecular hydrogen transfer in H(3)M-NCH has been definitely ruled out. Head-to-tail dimeric species [H(3)M-(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), CH(4), and C(2)H(6) from X(3)M-(NC)R adducts is very favorable thermodynamically; by contrast, elimination of HCl and CH(3)Cl 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,CH(3) and their presence in the reactor media should not be neglected. Moderate stability of [HMCH(2)NH](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.