| Abstract
| - Structuralstudies show that, in the solid state, the complexes[{HB(Pz3R,4R,5R)3}Ir(COD)](Pz = pyrazolyl, 3R and 5R = Me or othersubstituent, COD = cycloocta-1,5-diene) contain four-coordinateiridium(I) with an η2-pyrazolylborate, whileiridium(I) in [{HB(Pz)3}Ir(COD)]is five-coordinate with an η3-pyrazolylborate.However, equilibria between corresponding four- andfive-coordinate species are established in solution.Interestingly, the pyrazolyl groups in[{HB(Pz3Me)3}Ir(COD)]undergo 1,2-borotropic shifts, successively forming[{HB(Pz3Me)2(Pz5Me)}Ir(COD)]and[{HB(Pz3Me)(Pz5Me)2}Ir(COD)].
- The compounds [Tp3R,4R,5RIr(COD)] (COD =cycloocta-1,5-diene; Tp3R,4R,5R =hydrotris(pyrazolyl)borate (1),hydrotris(3-methylpyrazolyl)borate (2),hydrotris(3-isopropylpyrazolyl)borate (3),hydrotris(3,5-dimethylpyrazolyl)borate,hydrotris(3-(trifluoromethyl)-5-methylpyrazolyl)borate,hydrotris(3-phenyl-5-methylpyrazolyl)borate, hydrotris(3,5-diisopropylpyrazolyl)borate,hydrotris(3,4,5-trimethylpyrazolyl)borate,hydrotris(4-chloro-3,5-dimethylpyrazolyl)borate (9),hydrotris(4-bromo-3,5-dimethylpyrazolyl)borate) were preparedand characterized by IRand NMR spectroscopy. The X-ray crystal structure of9·2MeOH (triclinic, space group P1̄(No. 2); a = 10.044(1) Å, b = 11.186(2) Å, c =15.499(3) Å; α = 77.90(1)°, β = 73.23(1)°,γ = 66.89(1)°; Z = 2; R = 0.0276for2469 observed reflections) shows that iridium is four-coordinate withan η2-hydrotris(pyrazolyl)borate. TheX-raycrystal structure of 1 (triclinic, space groupP1̄ (No. 2); a = 7.345(1) Å,b = 7.645(1) Å, c = 15.893(5) Å;α =103.17(4)°, β = 90.30(2)°, γ = 93.50(3)°;Z = 2; R = 0.0433 for 2606 observedreflections) shows that iridiumis five-coordinate with an η3-bondedtris(pyrazolyl)borate. Equilibria between correspondingfour- (η2-Tp3R,4R,5R)and five-coordinate (η3-Tp3R,4R,5R) speciesof all the complexes are established in solution. The complexcontainingthe ligand HB(Pz3Me)3 (Pz = pyrazolylgroup) (2) rearranged first to the corresponding complexwith HB(Pz3Me)2(Pz5Me) and then into that withHB(Pz3Me)(Pz5Me)2.However, 3, which containsHB(Pz3iPr)3,gave only the complexwith coordinatedHB(Pz3iPr)2(Pz5iPr).
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