Rhodium catalysed rearrangement of 1,2-diphenylhydrazine to o-semidine

Abstract

Rearrangement of 1,2-diphenylhydrazine occurs exclusively to o-semidine in the presence of a rhodium catalyst with o-semidine bonding to rhodium(i) as a bidentate ligand.

Co-ordination of hydrazine and substituted hydrazines on reaction with [Rh2(CO)4Cl2] and disproportionation of 1,2-N2H2Ph2

“…We have previously reported the exclusive rearrangement of 1,2-N 2 H 2 Ph 2 to o-semidine (2-NH 2 C 6 H 4 NHPh) which becomes catalytic when there are two vacant sites on rhodium. 13 We now find that disproportionation of 1,2- Table 3 Selected bond lengths (Å) and angles (Њ) for complexes 1b and 1c…”

“…For the less heavily substituted hydrazines (Ia-Ie) there is excellent low-temperature NMR spectroscopic evidence ( 13 C and 15 N, see Tables 1 and 2 respectively) that the first formed product is 1 which is maximised at a ratio of [Rh 2 -(CO) 4 Cl 2 ] : I = 1 : 1. Thus, for complexes containing symmetrical hydrazines, (1a and Ic), there are two carbonyl resonances and, using 15 N 2 H 4 , only the lower-field resonance [δ(CO) 185.4] shows further coupling; as a result, this resonance must be due to the CO trans to the hydrazine [ 1 J( 103 Rh᎐ 13 CO) 65.8 and 2 J( 15 N᎐ 13 CO) 12.9 Hz] and the 15 N-{H} resonance of 1a and 1c is a single doublet upfield from that of the free hydrazine with At room temperature the 15 N-{ 1 H} NMR spectra are severely broadened and only one doublet is observed in the 13 CO region of the 13 C NMR spectrum of complexes 1a-1e. This suggests that the formation of 1 is reversible in solution at room temperature.…”

“…Complex 2f is the first example containing Me 2 NNMe 2 but, in this case, ready Scheme 1 Reaction products resulting from addition of hydrazine and increasingly substituted hydrazines (L) to decomposition occurs in solution at room temperature presumably because of the proximity of six β-H from the co-ordinated Me 2 N groups to the metals. At room temperature there is only one 13 CO NMR resonance for complexes 2a-2f due to the rapid site exchange of L and chloride. However, at low temperature two well resolved carbonyl resonances are observed (Table 4) due to the cis configuration and this is consistent with the presence, in all cases, of two equally intense ν(CO) bands in the infrared spectrum.…”

“…The progressive addition of hydrazine and the following increasingly substituted hydrazines L (N 2 H 4 Ia, H 2 NNHMe Ib, H 2 NNHPh Ie, H 2 NNMe 2 Id, or MeHNNHMe Ic) to [Rh 2 (CO) 4 Cl 2 ] resulted in the initial formation of [{Rh(CO) 2 Cl} 2 (µ-L)] 1 followed by the formation of cis-[Rh(CO) 2 L(Cl)] 2; analogous mononuclear complexes were formed directly on addition of the more heavily substituted hydrazines Me 2 NNMe 2 IIf and H 2 NNPh 2 IIg, but addition of 1,2-N 2 H 2 Ph 2 IIIh to [Rh 2 (CO) 4 Cl 2 ] resulted in disproportionation of the hydrazine and formation of cis-[Rh(CO) 2 (NH 2 Ph)Cl] 3 and cis-[Rh(CO) 2 (PhN᎐ ᎐ NPh)Cl] 4. The above complexes have been spectroscopically characterised by IR and 13 C/ 15 N NMR measurements. X-Ray structural analysis on [{Rh(CO) 2 Cl} 2 (µ-L)] (L = H 2 NNHMe or MeHNNHMe) confirmed that L adopts a µ-η 1 : η 1 -mode of bonding with a cisoid arrangement of the Rh(CO) 2 Cl groups about the N᎐N bond.…”

Rearrangements of Hydrazo, Azoxy and Azo Compounds: Kinetic, Product and Isotope Studies

“…One recent fascinating example of semidine formation is the exclusive formation of osemidine 6 when hydrazobenzene 1 is treated with a rhodium catalyst in dichloromethane solution; the o-semidine bonds to rhodium as a bidentate ligand, and presumably the geometrical requirements for this ensure that it is the preferred rearrangement product in this case 27 The reaction of 4, 4 -diiodohydrazobenzene (21) was used to investigate the acidcatalyzed disproportionation which accompanies many benzidine rearrangements 19 19 . Thus N−N bond breaking and C−C bond forming are both taking place at the transition state, and the rearrangement mechanism is probably exactly the same as for hydrazobenzene itself.…”