Dangling phosphine complexes: Phosphine exchange in pentacarbonyl tungsten complexes of bis(diphenylphosphinomethyl)phenylphosphine

• Reactions of [W(CO)5(NH2Ph)] with Ph2PCH2PPhCH2PPh2 led to six new complexes.
• Characterization included X-ray structures for three complexes.
• Intramolecular exchange rates for coordinated and pendant phosphines are reported.
• A mechanism for linkage isomerization is presented.
• A through-space contribution is proposed to partially account for 4JPC coupling.

The reaction of [W(CO)5NH2Ph] with Ph2PCH2PPhCH2PPh2 under mild conditions and stoichiometric control leads to two sets of linkage isomers: [(OC)5W{κ1-PPh(CH2PPh2)2}] 6a and [(OC)5W(κ1- PPh2CH2PPhCH2PPh2)] 6b; [(OC)5W{μ-PPh2CH2PPh(CH2PPh2)}W(CO)5] 7a and [(OC)5W(μ-PPh2CH2PPhCH2PPh2)W(CO)5] 7b. Isomers 6a and 6b exist in solution in equilibrium with K = 4.35 for 6b/6a in CDCl3 at 55 °C. Under the same conditions, the rate of isomerization of 6a to 6b is 4.32 × 10−6 s−1. Isomerization is thought to proceed by an initial attack of a carbonyl group by a pendant phosphine followed by ring opening and a 1,2-phosphine shift. At higher temperatures, chelated complexes with four- and six-membered rings are formed: [(OC)5W{μ-κ1-, κ2-PPh2CH2 (PhPCH2PPh2)W(CO)4 }] 9a, [(OC)5W{μ-κ1-, κ2-PPh (CH2PPh2)2}W(CO)4 }] 9b, and [(OC)4W{κ2-(PPh2CH2)2PPh}] 10b. X-ray crystal structures of 6a, 7b, and 9b have been determined.

The linkage isomers, [(OC)5W{κ1-PPh(CH2PPh2)2}] 6a and [(OC)5W(κ1-PPh2CH2PPhCH2PPh2)] 6b, exist in equilibrium (K = 4.35) in CDCl3 at 55 °C. The plot displays the increase in concentration of the more stable 6b as the concentration of 6a decreases. The structure of 6a shows two pendant phosphine arms, with one near and one away from the equatorial carbonyl plane. It is believed that the first step of the isomerization mechanism involves interaction of a pendant phosphine with a carbonyl group.Figure optionsDownload as PowerPoint slide