Protonation and deprotonation reactions of triruthenium nona- and octa-carbonyl clusters containing a µ3-2-amido-6-methylpyridine (µ3-ampy) ligand. X-Ray structures of [Ru3(µ-H)2(µ3-ampy)(CO)9][BF4] and of one of the two isolated isomers of [Ru3(µ-H)2(µ3-ampy)(CO)8(PPh3)][BF4]

Abstract

The complex [Ru₃(µ-H)(µ₃-ampy)(CO)₉](1)(Hampy = 2-amino-6-methylpyridine) reacts with HBF₄·OEt₂ to give the dihydride [Ru₃(µ-H)₂(µ₃-ampy)(CO)₉][BF₄](2), the structure of which has been determined by X-ray diffraction [monoclinic, space group C2/c, a= 23.468(6), b= 15.524(6), c= 15.283(3), β= 122.83(2)°, Z= 8]. Compound (2) reacts with NEt₃ regenerating (1) and with potassium methoxide giving a mixture of (1) and two isomers [(3) and (4)] of the methoxycarbonyl complex [Ru₃(µ-H)₂(µ₃-ampy)(CO₂Me)(CO)₈]. Complexes (1) and (2) react with PPh₃ to give [Ru₃(µ-H)(µ₃-ampy)(CO)₈(PPh₃)](5) and [Ru₃(µ-H)₂(µ₃-ampy)(CO)₈(PPh₃)][BF₄](6), respectively. In both cases substitution has taken place selectively at an equatorial position cis to the NH fragment and cis to one hydride and, in the case of complex (2), on the Ru atom bonded to only one hydride ligand. Complex (5) undergoes protonation with HBF₄·OEt₂ to give [Ru₃(µ-H)₂(µ₃-ampy)(CO)₈(PPh₃)][BF₄](7). The X-ray structure of (7)·OEt₂[triclinic, space group P, a= 10.657(5), b= 12.318(3), c= 16.622(3)Å, α= 99.14(2), β= 104.18(1), γ= 92.76(1)°, Z= 2] shows that the PPh₃ ligand is now on the Ru atom bonded to the two hydrides and trans to the hydride which spans the edge bridged by the amido group. Compounds (6) and (7) are isomers; the former can be converted into the latter upon heating in refluxing tetrahydrofuran. Treatment of complex (7) with NEt₃ or potassium methoxide results in deprotonation giving (5). However, although the reaction of (6) with NEt₃ also gives (5), the reaction of (6) with potassium methoxide leads to the methoxycarbonyl complex [Ru₃(µ-H)₂(µ₃-ampy)(CO₂Me)(CO)₇(PPh₃)](8). Arguments are presented which suggest that in the reactions leading to (3), (4), and (8), the attack of the methoxide ion takes place at equatorial CO ligands bonded to the ruthenium atoms which are attached to two hydrides. Proton and ³¹P-{¹H} n.m.r. and i.r. spectra of all the compounds are also included and discussed in relation to their structures.