Gold(I) and Related Heterometallic Derivatives of Dimolybdenum Complexes with Asymmetric Phosphinidene Bridges

The phosphinidene-bridged complexes
[Mo2Cp2(μ-κ1:κ1,η6-PR*)­(CO)2] (1), [Mo2Cp2(μ-κ1:κ1,η4-PR*)­(CO)3] (2), [Mo2Cp­(μ-κ1:κ1,η5-PC5H4)­(η6-HR*)­(CO)2] (3), and [Mo2Cp2(μ-κ1:κ1-PH)­(η6-HR*)­(CO)2] (4) were examined as precursors
of heterometallic gold­(I) and related
derivatives (Cp = η5-C5H5,
R* = 2,4,6-C6H2tBu3). These complexes reacted with [AuCl­(THT)] to give
the corresponding derivatives [AuMo2ClCp2(μ-κ1:κ1:κ1,η6-PR*)­(CO)2], [AuMo2ClCp2(μ-κ1:κ1:κ1,η4-PR*)­(CO)3] (Au–Mo = 2.8493(6) Å),
[AuMo2ClCp­(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)2(η6-HR*)], and [AuMo2ClCp2(μ3-PH)­(CO)2(η6-HR*)] formally resulting from the addition of an acceptor
AuCl moiety to the short Mo–P bond of the parent substrates
almost perpendicular to the corresponding Mo2P plane. The
chloride ligand was easily displaced upon reaction of the PC5H4-bridged gold complex with K­[MoCp­(CO)3] to
give the tetranuclear derivative [AuMo3Cp2(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)5(η6-HR*)] (Au–Mo = 2.711(2) and 2.807(2) Å). Compound 1 also reacted with HgI2 to give a hexanuclear
complex [HgMo2Cp2(μ-I)­I­(μ-κ1:κ1,η6-PR*)­(CO)2]2 containing dative Mo→Hg bonds (2.820(1) and
2.827(1) Å), whereas complex 3 gave the μ3-PR bridged complex [HgMo2CpI2(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)2(η6-HR*)]. Complexes 1 to 4 also reacted easily
with [AuL­(THT)]­PF6 (L = THT, P­(p-tol)3, PMe3, PiPr3) to give the corresponding cationic trinuclear derivatives [AuMo2Cp2(μ-κ1:κ1:κ1,η6-PR*)­(CO)2L]­(PF6) (Au–Mo = 2.8080(3) Å for L = P­(p-tol)3), [AuMo2Cp2(μ-κ1:κ1:κ1,η4-PR*)­(CO)3L]­(PF6), and [AuMo2Cp­(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)2(η6-HR*)­{P­(p-tol)3}]­(PF6). The
blue, analogous PH-bridged complexes were more conveniently isolated
as tetra-arylborate salts [AuMo2Cp2(μ3-PH)­(CO)2(η6-HR*)­L]­(BAr′4) (Au–Mo = 2.8038(6) Å for L = PiPr3; Ar′= 3,5-C6H3(CF3)2]. Compounds 1, 3,
and 4 reacted readily with the cation [Au­(THT)2]+ (as PF6– or BAr′4– salts) in a 2:1 ratio to give respectively
the corresponding pentanuclear derivatives [Au­{Mo2Cp2(μ-κ1:κ1:κ1,η6-PR*)­(CO)2}2]­(PF6), [Au­{Mo2Cp­(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)2(η6-HR*)}2]­(PF6) (Au–Mo = 2.7975(7) and 2.8006(7) Å), and [Au­{Mo2Cp2(μ3-PH)­(CO)2(η6-HR*)}2]­(BAr′4) (Au–Mo
= 2.8233(8) and 2.8691(7) Å). Related silver complexes were obtained
from the reaction of 3 and 4 with [AgCl­(PPh3)]4 after spontaneous symmetrization, while reaction
of 1 with [Cu­(NCMe)4]­PF6 in a 2:1
ratio yielded the analogous copper complex [Cu­{Mo2Cp2(μ-κ1:κ1:κ1,η6-PR*)­(CO)2}2]­(PF6). All the above cationic gold complexes having (μ-κ1:κ1:κ1,η6-PR*) ligands (but not the copper complex) rearranged into [Au­{Mo2Cp­(μ-κ1:κ1:κ1,η5-PC5H4)­(CO)2(η6-HR*)}2]­(PF6) in
refluxing 1,2-dichloroethane solution.