A Novel Route to Formaldehyde and Thioformaldehyde Rhodium Complexes

Abstract

The acetoxymethyl rhodium compounds [(η 5 -the formaldehyde compounds [(η 5 -C 5 R 5 )Rh(η 2 -CH 2 O)(L)] (24-27). The related thioformaldehyde complexes [(η 5 -C 5 R 5 )Rh(CH 2 OAc)(L)I] (4, 13-16) which were prepared from the chloromethyl derivatives [(η 5 -C 5 R 5 )Rh(CH 2 Cl)(L)I] and C 5 Me 5 )Rh(η 2 -CH 2 S)(L)] (46, 47) and [(η 5 -C 5 H 5 )Rh(η 2 -CH 2 S)(PMe 3 )] (50) were obtained on a similar route. Studies sodium acetate in benzene/acetic acid as solvent, reacted with AgPF 6 to give the chelate complexes [(η 5 -C 5 R 5 )Rh{κ 2 -on the reactivity of the formaldehyde derivatives revealed that the Rh-CH 2 O bond is rather labile and the CH 2 O ligand C,O-CH 2 OC(Me)O}(L)]PF 6 (19-23) in excellent yields. Treatment of these complexes with KOH in methanol led to easily converted to a CO group. the elimination of the acetyl group and to the formation of ResultsIn a series of papers we have recently shown [1] that cobalt and rhodium half-sandwich type complexes, which contain Preparation of RhCH 2 OAc PrecursorsMI(CH 2 I) as a molecular unit, can be transformed to the corresponding thio-, seleno-, and telluroformaldehydeThe carbenoide rhodium complex 1, which can easily be metal derivatives upon treatment with SH Ϫ , SeH Ϫ , and prepared from [C 5 Me 5 Rh(CO) 2 ] and CH 2 I 2 , [4] reacts quite TeH Ϫ , respectively (see Scheme 1). Due to the lone electron smoothly in polar solvents with sodium acetate. While in pairs at the chalcogen atom of the CH 2 E ligand, these comacetone a mixture of products is formed, the reaction of 1 pounds behave as Lewis bases and react with in situ generwith excess NaOAc in methanol leads to the methated 16-electron fragments such as [W(CO) 5 ] or [(η 5oxymethyl compound 2 in good yield. In contrast, the start-C 5 H 5 )Mn(CO) 2 ] to give dinuclear hetero-metallic coming material 1 and NaOAc react in ethanol to give two plexes with the aldehyde CH 2 E in a bridging position. [1d] [2] products 3 and 4 (see Scheme 2), which could be separated First attempts to complete the series of compounds [(η 5by chromatographic techniques. Although the desired ace-C 5 R 5 )M(η 2 -CH 2 E)(L)] by those with E ϭ O failed. The retoxy derivative 4 is the dominating species provided that an action of the respective precursor [(η 5 -C 5 R 5 )M(L)(LЈ)] with excess of sodium acetate is used, the separation of the two monomeric formaldehyde was rather slow and in most cases compounds on Al 2 O 3 results in the partial conversion of 4 led to a mixture of products among which the carbonyl complexes [(η 5 -C 5 R 5 )M(CO)(L)] were the dominating spe-cies. Therefore, we had to develop a different synthetic route. The present paper describes that for M ϭ Rh the key to success was the preparation of metalated acetic acid derivatives [Rh]CH 2 OC(O)CH 3 as intermediates which could be converted in two steps to the coordinated formaldehyde ligand. Some related results to this work were already reported. [3] Scheme 1Eur.