Inorganica Chimica Acta, 97 (1985) 19-23 19 Di(C1-pyrazolate)bis(pentamethylcyclopentadienyl)rhodium Complexes. Molecular Structure of [ {Rh(C,Me,)(pz)} l(~-pz)Zl (pz = pyrazolate) LUIS A. ORO, DANIEL CARMONA, M. PILAR LAMATA Departamento de Quimica Inorga’nica, Universidad de Zaragora, Saragossa, Spain CONCEPCI6N FOCES-FOCES and FI?LIX H. CAN0 Departamento de Rayos X, Instituto Rocasolano, C.S.I.C., Serrano, I1 9, M adrid- 6, Spain Received May 3, 1984 Abstract Neutral and cationic complexes of the general formulae [ {Rh(C,Me,)(Pz)}2@-Pz),] and [ {Rh- (C,MeS)(HPz)},@-Pz),](C10,)2 were prepared, starting from the dinuclear tri-p-hydroxo bridged complex [ {Rh(C,Mes)}&-0H),]C104. The inter- conversion between these two types of structures in acidic or basic media were studied. The structure of the title complex was established by X-ray crystallo- graphy. The complex crystallizes in the space group P2i/n with cell dimensions of a = 13.4979(4), b = 10.1424(2), c = 11.756.5(3) A, p = 103.765(2)“. The compound has an internal crystallographic center of symmetry relating the two halves of the molecule. The two rhodium atoms are separated by 4.103(l) A. neutral complexes with the formula [ {Rh(C,Me,)- (Pz)}&Pz),] (Pz = pz (I), Brpz (II) or idz (III))*. Molecular weight measurements on complexes (II) and (III) support this formulation**, and although the measured molecular weight of the pyrazole complex is intermediate between a mononuclear or dinuclear formulation, an X-ray structural analysis of complex (I) confirms the presence of either exo- bidentate and monodentate pyrazolate groups in the solid state. Furthermore, the ‘H NMR spectrum of complex (II), in CDCls, shows resonances assignable to exe-bidentate (6 = 8.12 ppm (s, 4H)) and mono- dentate (6 = 7.68 ppm (s, 2H); 7.37 ppm (s, 2H)) pyrazolate ligands along with the attributable to the &Me, groups (6 = 1.03 ppm (s, 30H)). Introduction There is an increasing interest in rhodium(I) com- plexes with pyrazole and pyrazolate-type ligands [l-l 11. In these compounds the pyrazolate anions act either as exe-bidentate [l-3, 5-8, 1 l] or mono- dentate ligands [6-81. On the other hand, the unusual formation of [ { Rh(C,Me,)((CF,),C,N,)} 2- (p(CFa),C,N,)(p-Ns)] by reaction of a dinuclear azidocyclopentadienyl complex with hexafluoro- but-2-yne has been reported [12]. This complex presents one bridging and two terminally-bonded azolate ligands. Interestingly, the addition of perchloric acid to complexes (II) or (III) gives rise to the protonation of the monodentate pyrazolate ligand with formation of 1{WC&W(H~)} 201-Pz)21(CQ)2 (Pz = Brpz (V), idz (VI)). As expected, the acidic hydrogen atom of the coordinated pyrazole ligand can be removed with ease, e.g. addition of potassium hydroxide to complex (V) regenerates the neutral complex (II). An alternative .and more direct method of preparing the cationic [ {Rh(C,Mes)(HPz)} z@-Pz)z] - (C1O4)2 complexes involves the reaction of [ (Rh- (C,Me,)}2(11-OH)31C104 with perchloric acid in the presence of an excess of the corresponding pyrazole ligand (Hpz (IV), HBrpz, Hidz, 3-methylpyrazole (HMepz) (VII), 3,5dimethylpyrazole (HMezpz) (VIII)). We report now that structurally-related complexes with two identical bridging pyrazolate groups can be readily obtained by a direct and general route. The IR spectra of the latter complexes present a v(N-H) band at cu. 3.350 cm-‘, along with the expected absorptions due to the coordinated organic ligands and the uncoordinated perchlorate groups. Results and Discussion The reaction of [ {Rh(C5Me,)}Z(p-OH)s]C104 [13] with an excess of pyrazole (Hpz), Q-bromo- pyrazole (HBrpz) or indazole (Hidz) and potassium hydroxide (l/8/8 or l/6/6) leads to the formation of *A generic pyrazole is indicated by HPz and unsubstituted pyrazole (CsH.+Nz) by Hpz. **Molecular weight measurements (CHC13). Complex (II): Found, 1004; Requires C32H3sN8Br4RhZ, 1060. Complex (III): Found, 953; Requires, C4aHs0NSRh2, 945. 0020-1693/85/$3.30 0 Elsevier Sequoia/Printed in Switzerland