188 F. Minzoni, C. Pelizzi and G. Predieri Phosphite complexes derived from Ferruccio Minzoni, Corrado Pelizzi and Giovanni Predieri* Transition Met. Chem. 7, 188-189 (1982) [M(Nz)z(dppe)2], M = Mo or W Istituto di Chimica generale ed inorganica dell'Universith e Centro di Studio per la Strutturistica diffrattometrica del C.N.R., Via M.D'Azeglio 85, 43100 Parma, Italy The complex trans-[Mo(Nz)2(dppe)2], (1), reacts with PhCI giving rise, through an homolytic reaction pattern, to chloro molybdenum complexes and to a variety of phenylated organic products (1). This observation prompted us to explore the potentiality of this reaction either by utilizing other aryl halides as radical sources (z) or, by introducing in the reaction mixtures, different substrates able to undergo radical attack (a). Thus, from anisole, we obtained the three isomers of methoxy- biphenyl and, from triethyl phosphite, we succeeded in syn- thesizing diethyl phenylphosphonate. In some of these latter experiments, an unexpected by-prod- uct was separated and was identified as [Mo(Nz)- {P(OEt)3}(dppe)2], (2) from analytical and i.r. data. This fact stimulated us to investigate the substitutions of (1) and [W(Nz)z(dppe)2], (3), with organic phosphites, and the results of this investigation are the argument of this report. As pointed out in a recent review (3), the displacement of diuitrogen generally occurs with ligands exhibiting similar bonding characteristics, particularly with carbon monoxide (4), isonitriles (5) and nitriles(6) in order to satisfy the electronic and steric requirements of the electron-rich, crowded Mo(dppe)2 site. From the electronic point of view, organophosphites possess good ~-aeceptor ability but their sizes are far from the sharp- ness of the previously mentioned ligands. In spite of this latter consideration, coordination to Mo(dppe)2 has been achieved, and some phosphite complexes have been obtained, even though in poor yields, according to the following procedures. A solution of (1) (0.1 mmol) and P(OEt)3 (0.4 mmol) in PhC1 (10 cm3) was stirred at room temperature for 72 h and the new Mo o complex (2) was separated, together with decom- position powder, by adding n-hexane. However, this reaction was not well reproducible and, in same experiments, only unreacted (1) and/or decomposition powders were obtained. Thus, in order to promote the dissociation of coordinated dinitrogen, we irradiated the reaction mixtures, the effect of light on the complex (1) being well known (7). Irradiation of Phil solutions of (1) or (3) in the presence of aromatic phos- * Author to whom all correspondence should be directed. phites, (PhO)3P and (p-C1C6H40)3P , gave complexes of the type [M{P(OR)3}2(dppe)2] in poor yields. On the other hand, prolonged irradiation in the presence of aliphatic phosphites yielded only uncharacterized powders. The impossibility of obtaining bis-(alkyl phosphite) complexes could be due to electronic effects, i.e. to the lower ~-acceptor ability of the alkyl phosphites compared with that of the aryl phosphites (s), steric effects being excluded owing to the slightly larger size of the latter (9). Characteristic data for the new phosphite complexes are given in the Table. A major feature of the i.r. spectra is the v(Nz) value in complex (2). In fact this band, in complexes of the trans- [Mo(Nz)(L)(dppe)2] type, appears to be sensitive to the z- acceptor ability of L. A n-electron withdrawing ligand would decrease the electron density at molybdenum, resulting in a lowering of back-donation from the metal to the dinitrogen ligand. This would be reflected in an increase of the v(Nz) value. In fact, v(N2) occurs at 1990 cm -1 in (2), 1978 cm -1 in (1) (a), 1930-1965 cm -1 (depending on the nature of X) in [Mo(Nz)(p-NCC6H4X)(dppe)z] (61, 1910 cm -1 (R = Me), 1915 cm -a (R = Et) in [Mo(Nz)(NCR)(dppe)z] (6) and 2110, 2080era -a (crystal packing splitting) in [Mo(Nz)(CO)- (dppe)2] 0a/. As expected, the effect of triethyl phosphite on v(Nz) is intermediate between that of CO and organonitriles, in agreement with its intermediate zt-acceptor ability. As regards the other complexes (4-7), the band splitting, due to the P-O-C system, observed in the tungsten com- plexes, can be ascribed to crystal packing effects, if we assume the retention of the trans-configuration in the formation of these compounds. Experimental All reactions were carried out under N2 using standard inert atmosphere techniques. Reagent grade organic solvents were dried by distillation from suitable drying agents. Complex (1) was prepared, from MoC15, by the literature method (lz) and complex (3), directly from WC16, according to a similar proce- dure (13). Commercially available organo-phosphites (Strem) Table Characterization data for the phosphite complexes a). Compoundb) Colour Selected i.r. bands (P)-O-Cc) P-O-(C) c) v(Nz) P(OR)3 rings dppe rings (2) [Mo(Nz)(tep)(dppe)2] brick red f 1040ms 932rns 1990vs - 1432s / 1027ms (4) [Mo(tpp)z(dppe)z] brown 1205vs 885vs - 1489vs 1432s (5) [Mo(tcpp)2(dppe)2] light brown 1203vs 880s - 1482vs 1431s (6) [W(tpp)2(dppe)z] light orange ~ 1220s ~ 877s - 1490vs 1431s [ 1188s [ 890s (7) [W(tcpp)2(dppe)2] 2C6H 6 orange ~" 1218s J883s - 1482vs 1430s [ 1192s [ 871s ") All reported complexes gave satisfactory elemental (C, H, N) analyses; b) tep = (EtO)3P; tpp = (PhO)3P; tcpp = (p-CIC6H40)3P; c) These assignments are only schematic. For a discussion of the vibrational behaviour of the P-O-C grouping, see ref. 10. 0340-4285/82/0306--0188502.50/0 Verlag Chemie GmbH, D-6940 Weinheim, 1982