Cationic Rh^I Complexes of Azulenes and Their Catalytic Activity on the Formation of Heptalene‐1,2‐dicarboxylates from Dimethyl Acetylenedicarboxylate and Azulenes

Abstract

Dcdicated tu Duilio Arigoni on the occasion of his 65th birthday (2. VIII.93) [Rh'(q 5-azulene)(cod)]+BF; complexes 3 a s (cod = (Z,Z)-cycloocta-1 ,S-diene) have been synthesized by reaction of [Rh'(cod)]+BF; in THF with the corresponding azulenes la-g ( Table I ) . The structure of [Rh'(cod)(q5-guaiarulene)]+BF~ (3a) has been determined by X-ray diffraction analysis ( Fig. I and 2). The Rh-atom is oriented above the five-membered ring of the azulene with almost equal Rh-C distances to all five C-atoms of the ring. The (Z,Z)-cycloocta-1,s-diene ring occurs in two enantiomorphic distorted (C2u+C2) tub conformations in the crystals (Fig. 3 ) . In CDCI, solution, the cod ligand in the complexes 3 shows a dynamic behavior on the 'H-NMR time scale which is best explained by rotation of the cod ligand relative to the azulene ligands around an imaginary cod-Rh-azulene axis. The new complexes 3 catalyze the formation of heptalene-1,2-dicarboxyIates 2 from dimethyl acetylenedicarboxylate (ADM) and the corresponding azulenes 1 just as effectively as [RuH,(PPh,),] and the analogous [RhH(PPh,),] complex in MeCN solution (Tahle 3 ) . On grounds of simplicity, 3 can be generated in sifu, when [RhCl(cod)I2 is applied as catalyst (Table 3 ) .Introduction. -Recently, we have shown that the yield of heptalene-l,2-dicarboxylates 2 formed from azulenes 1 and dimethyl acetylenedicarboxylate (ADM) in apolar solvents at temperatures > 180" can be improved substantially, when the reaction is carried out in the presence of a catalytic amount of [RuH,(PPh,),] in a polar aprotic solvent such as MeCN (Scheme 1 ) [l]. The reaction of l-(tert-butyl)-4,6,8-trimethylazulene with ADM in the presence of the catalyst yielded, even at 25", dimethyl 11-(tertbutyl)-2,4, 6-trimethyltricyclo[6.2.2.01 ']dodeca-2,4,6,9,11 -pentaene-9,1O-dicarboxylate, which represents the Diels-Alder-type adduct of ADM and the five-membered ring of the azulene. Since this type of adduct is also the established primary intermediate in the

Cationic (Azulene)(diene)rhodium(I) Complexes: Spectroscopic, Dynamic, and Catalytic Properties

“…Synthesis of the Complex Salts. The procedure as described in [1] (6) (6) 7)); 113.9 (d, 1 J(3a, 103 Rh) 1 J(8a, 103 Rh) 3.1, C(3a), C(8a)); 105.0…”

“…± Some years ago, we reported about the synthesis and characterization of [Rh I (h 5 -azulene)(cod)][BF 4 ] complex salts 3 (cod (1Z,5Z)-cycloocta-1,5-diene; cf. Table 1), which showed the azulenes coordinated with their five-membered ring to the metal atom [1]. Their synthesis is easy, and the cationic Rh I complexes are stable in the solid state, even under normal exposure to air over longer periods of time (several years).…”

“…Syntheses. The new complexes 3 ± 5 were synthesized in the same manner as described in [1]. The precursor cations, [Rh I (diene)] and [Ir I (cod)] , were generated in THF from the corresponding dimeric m-dichloro complexes by addition of AgBF 4 (Scheme 1).…”

“…The main structural difference between cod and nbd as ligands has its root in the skeletal flexibility of the former that allows the adoption of chiral conformations also in the complexes (cf. [1]) and the complete skeletal rigidity of the latter that preserves its local C 2v symmetry in the complexes (see below).…”

“…) Indeed, both complex forms of 3a were found in the X-ray crystal-structure analysis of 3a (cf [1]. and below).…”