Abstract:A synthetic methodology to obtain square-planar carbenerhodium (1)

A series of (diazoalkane)rhodium(I) compounds of the general composition trans-[RhCl(N2CRR‘)(PiPr3)2] with R = R‘ = Ph, p-C6H4Me, p-C6H4Cl and R = Ph, R‘ = p-C6H4Me, o-C6H4Me, CH3, CH2Ph, CF3 has been prepared from the dimer [RhCl(PiPr3)2]2 (1) and the diazoalkane. This preparative route has also been extended to complexes in which the N2C unit(s) of 1,4-C6H4{C(Ph)N2}2, 9-diazofluorene, 9,10-anthraquinone-9-diazide, and 3-methyl-1,4-naphthoquinone-1-diazide is (are) linked to a 14-electron [RhCl(PiPr3)2] fragment. While C(CO2Et)2N2 behaves as expected and affords upon treatment with 1 the complex trans-[RhCl{N2C(CO2Et)2}(PiPr3)2), CH(CO2Et)N2 reacts with the same starting material to give the dinitrogen derivative trans-[RhCl(N2)(PiPr3)2] (12). The reactions of trans-[RhCl(C2H4)(PiPr3)2] (2) with both N2CC4Cl4 and N2CC4Ph4 afford trans-[RhCl(N2CC4X4)(PiPr3)2] (X = Cl, Ph), and the same type of ligand exchange takes place by treatment of trans-[RhCl(C2H4)(SbiPr3)2] with N2CC4Cl4. The reactions of trans-[RhCl(N2CRR‘)(PiPr3)2] (3−7, where R and R‘ are aryl) with excess ethene give, instead of a disubstituted cyclopropane, exclusively the trisubstituted olefin CH3CHCRR‘. The reaction of 1 with PhC(R)NNH2 (R = Ph, Me) proceeds mainly by orthometalation to yield the six-coordinate rhodium(III) complexes [Rh(H)Cl{κ2-C,N-C6H4C(NNH2)R}(PiPr3)2]; of these, that with R = Ph reacts with Al2O3 to give trans-[RhCl(N2CPh2)(PiPr3)2] and 12. The alkynylrhodium(I) derivatives trans-[Rh(C⋮CX)(C2H4)(PiPr3)2] (X = H, tBu) behave similarly to 2 and afford upon treatment with Ph2CN2 and C12H8CN2 the corresponding diazoalkane compounds trans-[Rh(C⋮CX)(N2CRR‘)(PiPr3)2] by ligand exchange. The reaction of 2 with the diazo ketones RC(O)C(Ph)N2 (R = Ph, Me) leads to complexes of the general composition [RhCl{N2C(Ph)C(O)Ph}(PiPr3)2], in which the diazo ketone is probably coordinated in a chelating fashion to the metal center. The keto ester derivative (CH3)2CHCH2CH2C(O)C(CO2Me)N2 reacts with 2 to give a mixture of two isomers, one of which could be separated by fractional crystallization. The supposed chelating bonding mode of the diazo ligand in this compound via the terminal nitrogen and the keto oxygen could be confirmed by an X-ray crystal structure analysis.

A series of carbenerhodium(I) complexes of the general composition [(eta5-C5H5)Rh(=CRR')(L)] (2a-2i) with R = R'= aryl and L = SbiPr3 or PR3 has been prepared from the square-planar precursors trans-[RhCl(=CRR')(L)2] and NaC5H5 in excellent yields. Reaction of the triisopropylsibane derivative 2a. which contains a rather labile Rh-Sb bond, with CO, PMe3, and CNR (R = Me, CH2Ph, tBu) leads to the displacement of the SbiPr3 ligand and affords the substitution products [(eta5-C5H5)Rh(=CPh2)(L)] (3-7). In contrast, treatment of the triisopropylphosphane compound 2c with CO and CNtBu leads to the cleavage of the Rh=CPh2 bond and gives besides [(eta5-C5H5)Rh(PiPr3)(L)] (10, 12) by metal-assisted C-C coupling diphenylketene Ph2C=C=O (11) or the corresponding imine Ph2C=C=NtBu (13). While the reaction of 2a, c with C2H4 yields [(eta5-C5H5)Rh(C2H4)(L)] (14, 15) and the trisubstituted olefin Ph2C=CHCH3 (16), treatment of 2a, c with RN3 leads to the cleavage of both the Rh-EiPr3 and Rh=CPh2 bonds and gives the chelate complexes [(eta5-C5H5)Rh(kappa2-RNNNNR)] (19, 20). The substitution products 3 (L=CO) and 4 (L= PMe3) react with an equimolar amount of sulfur or selenium by addition of the chalcogen to the Rh=CPh2 bond to generate the complexes [(eta5-C5H5)Rh(kappa2-ECPh2)(L)] (21-24) with thio- or selenobenzophenone as ligand. Similarly, treatment of 3 with CuCl affords the unusual 1:2 adduct [(eta5-C5H5)(CO)Rh(mu-CPh2)(CuCl)2] (25), which reacts with NaC5H5 to form [(eta5-C5H5)(CO)Rh(muCPh2)Cu(eta5-C5H5)] (26). The molecular structures of 3 and 22 have been determined by X-ray crystallography.

Dedicated to Professor Otto J. Scherer on the occasion of his 65th birthdayIn the course of investigations on the reactivity of carbenerhodium complexes trans-[RhCl( CR' 2 )(L) 2 ] (R' aryl; L PR 3 , AsR 3 , SbR 3 ) we recently observed [1] that these compounds react smoothly with olefins, CO, and isocyanides by C ± C coupling. While the reaction of 1 with ethene affords besides 2 exclusively 1.1-diphenylpropene (and not 1.1diphenylcyclopropane), treatment of 1 with CO forms the carbonyl complex 3 and diphenylketene (Scheme 1). [1,2] Since it is known from the work by the groups of Herrmann, Cutler, Roper, and others that reactions of both metal carbonyls with diazoalkanes and of metal carbenes with CO under pressure lead to ketene complexes, [3] we were inter-Scheme 1. L PiPr 3 .

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