Homo- and Heteropolynuclear Complexes Containing Bidentate Bridging 4‑Phosphino-N-Heterocyclic Carbene Ligands

The abnormal reaction of phosphaalkenes with N-heterocyclic carbenes (NHC) offers a convenient method to introduce new functionality at the backbone of an NHC. The 4-phosphino-substituted NHC (<b>1a</b>) derived from 1,3-dimesitylimidazol-2-ylidene (IMes) and MesPCPh₂ is shown to be an effective bifunctional ligand for Au­(I) and Pd­(II). Several new complexes are reported: <b>2a</b>: <b>1a</b>·Au_<i>C</i>Cl, <b>3a</b>: <b>1a</b>·(AuCl)₂, <b>4a</b>: [(<b>1a</b>)₂Au_<i>C</i>]­Cl, <b>5a</b>: [(<b>1a</b>·Au_<i>P</i>Cl)₂Au_<i>C</i>]­Cl], and <b>6a</b>: <b>1a</b>·(Pd_<i>C</i>) (Au_<i>P</i>Cl). The reaction of 4-phosphino-NHC <b>1b</b>, derived from 1,3-di­(cyclohexyl)­imidazol-2-ylidene (ICy) and MesPC­(4-C₆H₄F)₂, with (tht)­AuCl (2 equiv, tht = tetrahydrothiophene) affords the fascinating tetranuclear <b>5b</b> [(<b>1b</b>·Au_<i>P</i>Cl)₂Au_<i>C</i>]­[AuCl₂]. The molecular structure of <b>5b</b> features a close Au···Au contact (3.0988(4) Å) between the bis­(carbene)­gold­(I) cation and the dichloroaurate­(I) anion. The buried volumes (%<i>V</i>_bur) and Tolman cone angles for representative 4-phosphino-NHCs calculated from structural data are compared to related carbenes and phosphines. The molecular structures are reported for complexes <b>3a</b>, <b>4a</b>, <b>5b</b>, and <b>6a</b>

Aminoborane σ Complexes: Significance of Hydride Co-ligands in Dynamic Processes and Dehydrogenative Borylene Formation

Systems of the type [(<i>p</i>-cym)­Ru­(PR₃)­(H)­(H₂BN^<i>i</i>Pr₂)]⁺ (R = Cy, Ph) can be synthesized from (<i>p</i>-cym)­Ru­(PR₃)­Cl₂ and H₂BN^<i>i</i>Pr₂/Na­[BAr^<i>f</i>₄] and are best formulated as (hydrido)ruthenium κ¹-aminoborane complexes. VT-NMR measurements have been used to probe the σ-bond metathesis process leading to Ru–H/H–B exchange, yielding an activation barrier of Δ<i>G</i>^⧧ = 7.5 kcal mol^–1 at 161 K. Moreover, in contrast to the case for related non-hydride-containing systems, reactivity toward alkenes constitutes a viable route to a metal borylene complex via sacrificial hydrogenation

Aminoborane σ Complexes: Significance of Hydride Co-ligands in Dynamic Processes and Dehydrogenative Borylene Formation

Systems of the type [(<i>p</i>-cym)­Ru­(PR₃)­(H)­(H₂BN^<i>i</i>Pr₂)]⁺ (R = Cy, Ph) can be synthesized from (<i>p</i>-cym)­Ru­(PR₃)­Cl₂ and H₂BN^<i>i</i>Pr₂/Na­[BAr^<i>f</i>₄] and are best formulated as (hydrido)ruthenium κ¹-aminoborane complexes. VT-NMR measurements have been used to probe the σ-bond metathesis process leading to Ru–H/H–B exchange, yielding an activation barrier of Δ<i>G</i>^⧧ = 7.5 kcal mol^–1 at 161 K. Moreover, in contrast to the case for related non-hydride-containing systems, reactivity toward alkenes constitutes a viable route to a metal borylene complex via sacrificial hydrogenation