Articles Nitrogen-to-Metal Multiple Bond Functionalities: The Reaction of Calix[4]arene-W(IV) with Azides and Diazoalkanes Geoffroy Guillemot, Euro Solari, and Carlo Floriani* Institut de Chimie Mine ´ rale et Analytique, BCH, Universite ´ de Lausanne, CH-1015 Lausanne, Switzerland Corrado Rizzoli Dipartimento di Chimica, Universita ` di Parma, I-43100 Parma, Italy Received July 17, 2000 The [{calix[4]-(O) 4 }W(η 2 -C 6 H 10 )], 2, has been used as a source of W IV -d 2 center-bonded to an oxo surface, which has been modeled by the calix[4]arene tetraanion in the reaction with diazoalkanes and organic azides. The olefin is easily displaced by both substrates. The reaction with Ph 2 CN 2 led to the formation of metallahydrazone, [{calix[4]-(O) 4 }WdN- NCPh 2 ], 5, which binds Bu t NC inside the cavity, 6, or it can be reduced to a dinuclear W V derivative [W-W, 2.646(1) Å], where the two metals are bridged by a diphenylhydrazido ligand in complex 7,[{calix[4]-(O) 4 } 2 W 2 (µ-N-NdCPh 2 ) 2 Na 2 ]. The reaction of 2 with organic azides (RN 3 ) is strongly dependent on the nature of the R substituent at the azide functionality. The reaction with RN 3 [R ) SiMe 3 ; CPh 3 ] occurs at the metal in the exo position, leading to alkylimido derivatives [{calix[4]-(O) 4 }WdN-R] [R ) SiMe 3 , 8;R ) CPh 3 , 9], which bind inside the cavity Bu t NC, leading to 10 and 11, respectively. The reaction of 2 with PhN 3 , on the contrary, occurs inside the calixarene cavity, leading to the triazenido derivative [{µ-calix[4]-(O) 4 } 2 (WdN-NdNPh) 2 ], 12. The results of 2 with organic azides show that two different pathways are followed at the metal in the exo and endo positions. In the former case, for steric reasons, the 1,3 dipolar addition of the azide to the carbenoid metal precedes the formation of the alkylimido. In the case of PhN 3 , the size of the calix cavity prevents the same pathway. In the case of HN 3 the reaction is supposed to proceed with HN 3 binding the metal with the protonated nitrogen inside the cavity and decomposing to the imido functionality [{µ-calix[4]-(O) 4 } 2 (WdNH) 2 ], 13. An alternative synthetic route to arylimido derivatives of W VI has been reported. The reaction of [calix[4]-(ONa) 4 (THF) 2 ] with [p-tolyl- NtWCl 4 ] led to [µ-calix[4]-WtN-p-tolyl], 14, which is in equilibrium in solution with the corresponding dimeric form [{µ-calix[4]} 2 -WtN-p-tolyl], 15. Introduction A set of oxygen donor atoms, providing both σ and π electron donation to a metal center, is not appropriate for stabilizing any low oxidation state of a transition metal. This is, however, a synthetic advantage, since very reactive, unstable, low-valent metals produced in an oxygen donor atom environment can be generated in situ and intercepted by an appropriate reducible substrate. This event is probably occurring on metal- oxo surfaces displaying reactivities that are difficult to match using molecular compounds. 1 In this respect, metallacalixarenes are probably appropriate mole- cules for entering the game. 2 Reduction of metallacalix- arenes, 3 namely in the case of tungsten 4 and niobium, 5 * To whom correspondence should be addressed. (1) (a) Thomas, J. M.; Thomas, W. J. Principles and Practice of Heterogeneous Catalysis; VCH: Weinheim, Germany, 1997. (b) Gates, B. Catalytic Chemistry; Wiley: New York, 1992. (c) Mechanisms of Reactions of Organometallic Compounds with Surfaces; Cole-Hamilton, D. J., Williams, J. O., Eds.; Plenum: New York, 1989. (d) Kung, H. H. Transition Metal Oxides: Surface Chemistry and Catalysis; Elsevier: Amsterdam, The Netherlands, 1989. (e) Hoffmann, R. Solid and Surfaces, A Chemist’s View of Bonding in Extended Strucures; VCH: Weinheim, Germany, 1988. (f) Campbell, I. M. Catalysis at Surfaces; Chapman & Hall: London, U.K., 1988. (2) Floriani, C. Chem. Eur. J. 1999, 5, 19. (3) (a) Gutsche, C. D. Calixarenes; The Royal Society of Chemistry: Cambridge, U.K., 1989. (b) Gutsche, C. D. Calixarene Revisited; The Royal Society of Chemistry: Cambridge, U.K., 1998. (c) Calixarenes, A Versatile Class of Macrocyclic Compounds; Vicens, J., Bo ¨hmer, V., Eds.; Kluwer: Dordrecht, The Netherlands, 1991. (d) Bohmer, V. Angew. Chem., Int. Ed. Engl. 1995, 34, 713. (e) Wieser, C.; Dieleman, C. B.; Matt, D. Coord. Chem. Rev. 1997, 165, 93. (f) Roundhill, D. M. Metal Complexes of Calixarenes. In Progr. Inorg. Chem. 1995, 533. (g) Ikeda, A.; Shinkai, S. Chem. Rev. 1887, 97, 1713. (4) Giannini, L.; Solari, E.; Floriani, C.; Re, N.; Chiesi-Villa A.; Rizzoli, C. Inorg. Chem. 1999, 38, 1438. 607 Organometallics 2001, 20, 607-615 10.1021/om000612s CCC: $20.00 © 2001 American Chemical Society Publication on Web 01/23/2001