Synthesis, molecular structure, and reactivity of rhodium(I) complexes with diazoalkanes and related substrates as ligands

A series of (diazoalkane)rhodium(I) compounds of the general composition trans-[RhCl-(N 2 CRR')(PiPr 3 ) 2 ] with R = R' = Ph, p-C6H4Me, p-C6H4Cl and R = Ph, R' = p-C 6 H 4 Me, o-C 6 H 4 -Me, CH 3 , CH 2 Ph, CF 3 has been preparedfrom the dimer [RhCl(PiPr 3 ) 2 ] 2 (1) and the diazoalkane. This preparative route has also been extended to complexes in which the N 2 C unit(s) of 1,4-C 6 H 4 {C(Ph)N 2 } 2 , 9-diazofluorene, 9,10-anthraquinone-9-diazide, and 3-methyl-1,4-naphthoquinone-1-diazide is (are) linked to a 14-electron [RhCl(PiPr 3 ) 2 ] fragment. While C(CO 2 Et) 2 N 2 behaves as expected and affords upon treatment with 1 the complex trans-[RhCl{N 2 C(CO 2 Et) 2 }(PiPr 3 ) 2 ), CH(CO 2 Et)N 2 reacts with the same starting material to give the dinitrogen derivative trans-[RhCl(N 2 )(PiPr 3 ) 2 ] (12). The reactions of trans-[RhCl(C 2 H 4 )-(PiPr 3 ) 2 ] (2) with both N 2 CC 4 Cl 4 and N 2 CC 4 Ph 4 afford trans-[RhCl(N 2 CC 4 X 4 )(PiPr 3 ) 2 ] (X = Cl, Ph), and the same type of ligand exchange takes place by treatment of trans-[RhCl-(C 2 H 4 )(SbiPr 3 ) 2 ] with N 2 CC 4 Cl 4 . The reactions of trans-[RhCl(N 2 CRR')(PiPr 3 ) 2 ] (3-7, where R and R' are aryl) with excess ethene give, instead of a disubstituted cyclopropane, exclusively the trisubstituted olefin CH 3 CH=CRR'. The reaction of 1 with PhC(R)NNH 2 (R = Ph, Me) proceeds mainly by orthometalation to yield the six-coordinate rhodium(III) complexes [Rh-(H)Cl{κ 2 -C,N-C 6 H 4 C(NNH 2 )R}(PiPr 3 ) 2 ]; of these, that with R = Ph reacts with Al 2 O 3 to give trans-[RhCl(N 2 CPh 2 )(PiPr 3 ) 2 ] and 12. The alkynylrhodium(I) derivatives trans-[Rh(C≡CX)-(C 2 H 4 )(PiPr 3 ) 2 ] (X = H, tBu) behave similarly to 2 and afford upon treatment with Ph 2 CN 2 and C 1 2 H 8 CN 2 the corresponding diazoalkane compounds trans- [Rh(C≡CX)(N 2 CRR')(PiPr 3 ) 2 ] by ligand exchange. The reaction of 2 with the diazo ketones RC(O)C(Ph)N 2 (R = Ph, Me) leads to complexes of the general composition [RhCl{N 2 C(Ph)C(O)Ph}(PiPr 3 ) 2 ], in which the diazo ketone is probably coordinated in a chelating fashion to the metal center. The keto ester derivative (CH 3 ) 2 CHCH 2 CH 2 C(O)C(CO 2 Me)N 2 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.