Mixed-Donor Ligands: Pyrrolecarbaldehyde and Pyrrolecarbothioaldehyde σ-Organyl Complexes of Ruthenium(II) and Osmium(II)

Vilsmair salts have been used to prepare a series of thioaldehyde molecules conjugated
with a pyrrole ring (pyrrole substituents:  H, Me, Et). The reaction of 3,5-dimethyl-4-ethylpyrrole-2-carbothioaldehyde (HL4) with [RuHCl(CO)(PPh3)3] or [RuHCl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) in the presence of NaOMe leads to the complex [RuH(κ2-L4)(CO)(PPh3)2], in which the carbothioaldehyde ligand acts as a bidentate,
three-electron donor. The same approach yields the aryl, alkenyl, and alkynyl complexes [RuR(κ2-L4)(CO)(PPh3)2] (R = C6H5, CHCH2, CHCHPh, CHCHC6H4Me-4,
CHCHtBu, CHCHCPh2OH, CHCH(HO)C6H10, C(C⋮CPh)CHPh, C⋮CPh). The compound [Ru(CHCHCPh2OH)(κ2-L4)(CO)(PPh3)2] can be dehydrated by reaction with HBF4
to yield the vinylcarbene species [Ru(CHCHCPh2)(κ2-L4)(CO)(PPh3)2]BF4. The complexes
[RuR(κ2-L6)(CO)(PPh3)2] (R = H, CHCH2, CHCHC6H4Me-4, C(C⋮CPh)CHPh) were
prepared from pyrrole-2-carboxaldehyde (HL6), the oxygen analogue of the carbothioaldehyde
ligands. Additionally, the osmium ethenyl compounds [Os(CHCH2)(κ2-L4)(CO)(PPh3)2] and
[Os(CHCH2)(κ2-L6)(CO)(PPh3)2] were synthesized from [Os(CHCH2)Cl(CO)(BTD)(PPh3)2]
with either HL4 or HL6 in the presence of NaOMe. The crystal structures of the principal
ligand and three representative complexes are reported.