On the Transition Metal Complexation (Fischer-Type) of Phosphanylcarbenes Wolfgang W. Schoeller,* Dirk Eisner, Sonja Grigoleit, Alexander B. Rozhenko, and Alexander Alijah Contribution from the Fakulta ¨ t fu ¨ r Chemie der UniVersita ¨ t, Postfach 10 01 31, 33501 Bielefeld, Germany ReceiVed March 8, 2000. ReVised Manuscript ReceiVed July 20, 2000 Abstract: The formation of a Fischer-type transition metal complex with a W(CO) 5 fragment is evaluated for the phosphanylcarbenes, Arduengo-type carbenes, and Bertrand-type carbenes by means of quantum chemical investigations at a density functional level with effective core potential methods. Accordingly, the stabilities of the complexes depend strongly on the substitution pattern of the carbenic unit. Amino-substituted carbenes as well as the Arduengo-type carbene form stable transition metal complexes. The stabilities of the complexes decrease for the phosphanylcarbenes and are at a minimum for the hitherto unknown transition metal complexes of the push-pull-type carbene of Bertrand. The matter is analyzed in terms of distortion energies required to bring the carbene units into the geometrical standard state for complexation with the transition metal fragment. The arguments evaluated for the phosphanylcarbenes should hold equally well for other carbenes substituted with electropositive ligands. For the mono-phosphanylcarbenes, η 1 as well as η 2 structures are investigated. For the diphosphanylcarbenes, a new structural type of metal complexes is predicted in which the transition metal fragment is strongly bound to a cyclic structural valence isomer of the carbene. Introduction The first syntheses of isolable phosphanylcarbenes, I, was recorded some time ago by Bertrand and co-workers in a series of pioneering studies. 1-7 The stability of this type of carbenes was attributed to the amino groups at phosphorus and simul- taneously electron-withdrawing groups (SiR 3 , PR 3 (+), R ) alkyl, aryl) at the carbon atom. At the same time, another representative of a stable carbene, the imidazol-2-ylidene, II, was reported by Arduengo and co-workers. 8-11 In this type of structure, the electron-deficient divalent carbon center is π-con- jugated with two amino groups. Recently, a “mixed” carbene which contains a phosphanyl and an amino group was charac- terized 12 (Scheme 1). Regarding transition metal coordination, the two types of stable carbenes, I vs II, reveal a strikingly different behavior. The N-heterocyclic carbenes form very stable transition metal complexes with various early and late transition metal fragments. 13-18 An analysis of the peculiar bonds in these complexes shows only little metal f carbene π-back-donation, and yet the calculated bond strengths might be large (e.g., in ClAu-C carbene 19 ). Thus, the experimental investigations indicate that the Arduengo carbene bears bonding properties similar to those of the related Fischer carbene. 20 In contrast to II, transition metal complex formation of the Bertrand-type carbene I is * To whom correspondence should be addressed. E-mail: wolfgang@ tc.uni-bielefeld.de. (1) Baceiredo, A.; Bertrand, G.; Sicard, G. J. Am. Chem. Soc. 1985, 107, 4781-4783. (2) Igau, A.; Gru ¨ tzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am. Chem. Soc. 1988, 110, 6463-6466. (3) Gillette, G.; Baceiredo, A.; Bertrand, G. Angew. Chem. 1990, 102, 1486-1488; Angew. Chem., Int. Ed. Engl. 1990, 29, 1429. 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A.; Mihalios, D.; Elison, M.; Herdtweck, E.; Priermeier, T.; Kiprof, P. J. Organomet. Chem. 1995, 498,1-14. Hermann, W. A.; Fischer, J.; O ¨ fele, K.; Artus, G. R. J. J. Organomet. Chem. 1997, 530, 259-262. (14) Raubenheimer, H. G.; Cronje, S., van Rooyen, P. H.; Olivier, P. J.; Toerien, J. G. Angew. Chem. 1994, 106, 687-688; Angew. Chem., Int. Ed. Engl. 1994, 33, 672. (15) Hermann, W. A.; O ¨ fele, K.; Elison, M.; Ku ¨hn, F. F.; Roesky, P. W. J. Organomet. Chem. 1994, 480, C7. (16) Kuhn, N.; Kratz, T.; Bla ¨ser, D.; Boese, R. Inorg. Chim. Acta 1995, 238, 179-181. (17) Arduengo, A. J., III; Dias, H. V. R.; Calabrese, J. C.; Davidson, F. Organometallics 1993, 12, 3405-3409. (18) For further references, see: Hermann, W. A.; Ko ¨cher, C. Angew. Chem. 1997, 109, 2256-2282; Angew. Chem., Int. Ed. Engl. 1997, 36, 2162. (19) Boehme, C.; Frenking, G. Organometallics 1998, 17, 5809-5809. (20) Elschenbroich, Ch.; Salzer, A. Organometallchemie; Teubner Stu- dienbu ¨cher: Stuttgart 1986. Scheme 1 10115 J. Am. Chem. Soc. 2000, 122, 10115-10120 10.1021/ja000844i CCC: $19.00 © 2000 American Chemical Society Published on Web 09/29/2000