ABSTRACT
Three asymmetric diosmium(I) carbonyl sawhorse complexes have been prepared by microwave heating. One of these complexes is of the type Os2(µ-O2CR)(µ-O2CR')(CO)4L2, with two different bridging carboxylate ligands, while the other two complexes are of the type Os2(µ-O2CR)2(CO)5L, with one axial CO ligand and one axial phosphane ligand. The mixed carboxylate complex Os2(µ-acetate)(µ-propionate)(CO)4[P(p-tolyl)3]2, (1), was prepared by heating Os3(CO)12 with a mixture of acetic and propionic acids, isolating Os2(µ-acetate)(µ-propionate)(CO)6, and then replacing two CO ligands with two phosphane ligands. This is the first example of an Os2 sawhorse complex with two different carboxylate bridges. The syntheses of Os2(µ-acetate)2(CO)5[P(p-tolyl)3], (3), and Os2(µ-propionate)2(CO)5[P(p-tolyl)3], (6), involved the reaction of Os3(CO)12 with the appropriate carboxylic acid to initially produce Os2(µ-carboxylate)2(CO)6, followed by treatment with refluxing tetrahydrofuran (THF) to form Os2(µ-carboxylate)2(CO)5(THF), and finally addition of tri-p-tolylphosphane to replace the THF ligand with the P(p-tolyl)3 ligand. Neutral complexes of the type Os2(µ-O2CR)2(CO)5L had not previously been subjected to X-ray crystallographic analysis. The more symmetrical disubstituted complexes, i.e. Os2(µ-formate)2(CO)4[P(p-tolyl)3]2, (8), Os2(µ-acetate)2(CO)4[P(p-tolyl)3]2, (4), and Os2(µ-propionate)2(CO)4[P(p-tolyl)3]2, (7), as well as the previously reported symmetrical unsubstituted complexes Os2(µ-acetate)2(CO)6, (2), and Os2(µ-propionate)2(CO)6, (5), were also prepared in order to examine the influence of axial ligand substitution on the Os-Os bond distance in these sawhorse molecules. Eight crystal structures have been determined and studied, namely µ-acetato-1κO:2κO'-µ-propanoato-1κO:2κO'-bis[tris(4-methylphenyl)phosphane]-1κP,2κP'-bis(dicarbonylosmium)(Os-Os) dichloromethane monosolvate, [Os2(C2H3O2)(C3H5O2)(C21H21P)2(CO)4]·CH2Cl2, (1), bis(µ-acetato-1κO:2κO')bis(tricarbonylosmium)(Os-Os), [Os2(C2H3O2)2(CO)6], (2) (redetermined structure), bis(µ-acetato-1κO:2κO')pentacarbonyl-1κ2C,2κ3C-[tris(4-methylphenyl)phosphane-1κP]diosmium(Os-Os), [Os2(C2H3O2)2(C21H21P)(CO)5], (3), bis(µ-acetato-1κO:2κO')bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os-Os) p-xylene sesquisolvate, [Os2(C2H3O2)2(C21H21P)2(CO)4]·1.5C8H10, (4), bis(µ-propanoato-1κO:2κO')bis(tricarbonylosmium)(Os-Os), [Os2(C3H5O2)2(CO)6], (5), pentacarbonyl-1κ2C,2κ3C-bis(µ-propanoato-1κO:2κO')[tris(4-methylphenyl)phosphane-1κP]diosmium(Os-Os), [Os2(C3H5O2)2(C21H21P)(CO)5], (6), bis(µ-propanoato-1κO:2κO')bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os-Os) dichloromethane monosolvate, [Os2(C3H5O2)2(C21H21P)2(CO)4]·CH2Cl2, (7), and bis(µ-formato-1κO:2κO')bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os-Os), [Os2(CHO2)2(C21H21P)2(CO)4], (8).
ABSTRACT
In the title complex C34H20O6Os2 or (µ-η4-C4Ph4)Os2(CO)6, one Os atom is part of a metalla-cyclo-penta-diene ring, while the second Os atom is π-bonded to the organic portion of this ring. The distance of 2.7494â (2)â Å between the two Os atoms is typical of an Os-Os single bond. Three carbonyl ligands are attached to each Os atom and these six carbonyls adopt an eclipsed conformation. There are no bridging or semibridging CO groups. Two carbonyl ligands and all four phenyl groups are disordered over two slightly different positions for which each atom in the minor components is displaced less than 1â Å from the corresponding atom in the major components. The refined occupancies of the major com-ponents of the carbonyl ligands are 0.568â (16) and 0.625â (13), while those for the phenyl rings are 0.50â (3), 0.510â (12), 0.519â (18), and 0.568â (12).
