H⁺/AuPPh₃⁺Exchange for the Hydride Complexes CpMoH(CO)₂(L) (L = PMe₃, PPh₃, CO). Formation and Structure of [Cp(CO)₂(PMe₃)Mo(AuPPh₃)₂]⁺[BF₄]^-

Abstract

The reaction of CpMoH(CO)(2)L with AuPPh(3)(+)BF(4)(-) in THF at -40 degrees C proceeds directly to the MoAu(2) cluster compounds [CpMo(CO)(2)L(AuPPh(3))(2)](+)BF(4)(-) (L = PMe(3) (1), PPh(3) (2)) with release of protons. A 1:1 reaction leaves 50% of the starting hydride unreacted. At lower temperature, however, the formation of a [CpMo(CO)(2)(PMe(3))(&mgr;-H)(AuPPh(3))](+) intermediate is observed. This compound evolves to the cation of 1 and CpMoH(CO)(2)(PMe(3)) upon warming and is deprotonated by 2,6-lutidine to afford CpMo(CO)(2)(PMe(3))(AuPPh(3)). The X-ray structure of 1 can be described as a four-legged piano stool with the PMe(3) and the "eta(2)-(AuPPh(3))(2)" ligands occupying relative trans positions. [Cp(CO)(2)(PMe(3))Mo(AuPPh(3))(2)](+)[BF(4)](-) (M(r) = 1298.41): monoclinic, space group P2(1)/n, a = 18.1457(13) Å, b = 9.7811(7) Å, c = 26.096(2) Å, beta = 105.086(5) degrees, V = 4472.0(5) Å(3), Z = 4. The reaction of CpMoH(CO)(2)(PMe(3)) with 3 equiv of AuPPh(3)(+) affords a MoAu(3) cluster, [CpMo(CO)(2)(PMe(3))(AuPPh(3))(3)](2+) (3), in good yields under kinetically controlled conditions. Under thermodynamically controlled conditions, 3 dissociates extensively into 1 and free AuPPh(3)(+). It is proposed that the hydride ligand helps build higher nuclearity Mo-Au clusters. The difference in reaction pathways for the interaction of AuPPh(3)(+) with CpMoH(CO)(2)L when L = PR(3) or CO and for the interaction of CpMoH(CO)(2)(PMe(3)) with E(+) when E = H, Ph(3)C or AuPPh(3) is discussed. The lower acidity and greater aurophilicity of the [CpMo(CO)(2)L(&mgr;-H)(AuPPh(3))](+) intermediate when L = PMe(3) favor attack by AuPPh(3)(+) before deprotonation.

Catalytic Ionic Hydrogenations

“…[29] Norton determined that the pK a of [W(Cp)(CO) 2 -(PMe 3 )(H) 2 ] + in CH 3 CN was 5.6. [27] Comparison of this value with the pK a of about À0.1 in CH 3 CN for protonated acetone, [30] proceed cleanly, however, since the proton transfer step is followed by a fast hydride transfer from the neutral metal hydride [Eq.…”

Electrophilic Addition vs Electron Transfer for the Interaction of Ag+ with Molybdenum(II) Hydrides. 1. Reaction with CpMoH(PMe3)3 and the Mechanism of Decomposition of [CpMoH(PMe3)3]+

“…This has been the case for the particular complex CpMoH(CO) 2 (PMe 3 ), one of the rare mononuclear hydride complexes for which the comparative reactivity with both the proton and the AuPPh 3 + reagent has been investigated. 21 The silver ion has also been extensively investigated as an electrophilic reagent toward transition metal hydride complexes. The typical pathway is the attack at the M-H electron density, to afford complexes analogous to those obtained with the gold reagents (i.e., path b in Scheme 1).…”

“…The substitution of H + for AuPh 3 + typically affords more stable products. This has been the case for the particular complex CpMoH(CO) 2 (PMe 3 ), one of the rare mononuclear hydride complexes for which the comparative reactivity with both the proton and the AuPPh 3 + reagent has been investigated …”

[cis-{η2-(Ph3PAu)2}Ph3PCr(CO)4]·THF, featuring the shortest known separation between two Au metal centres in a heteronuclear Au2Mcluster

“…The title complex, (I), which is reported here, is therefore the ®rst example of a 2 -digold complex with chromium. The closest structurally characterized analogue to (I) is the cationic [ 2 -(Ph 3 PAu) 2 PMe 3 MoCp(CO) 2 ] complex reported by Gallasi et al (1997).…”

“…The shortening of AuÐAu distances in triangular MAu 2 cluster compounds has been linked to the electron density at the metal centre, M (Gallasi et al, 1997). A higher electron density on M corresponds to better interaction with electrophilic Ph 3 PAu fragments and also decreases the Au + ±Au + repulsion.…”