Nickel-Catalyzed Alkyne Cyclotrimerization Assisted by a Hemilabile Acceptor Ligand: A Computational Study

π-coordinating units incorporated in the supporting ligand of an organometallic complex may open up specific reactive pathways. The diphosphine ketone supported nickel complex [(p-tolL1)Ni(BPI)] (p-tol1; p-tolL1 = 2,2′-bis(di-p-tolylphosphino)benzophenone; BPI = benzophenone imine) has previously been shown to act as an active and selective alkyne cyclotrimerization catalyst. Herein, DFT calculations support an adaptive behavior of the ligand throughout the catalytic cycle, several elementary steps being assisted by coordination or decoordination of the C═O moiety. A comparison with related bi- and tridentate phosphine ligands reveals the key role of the hemilabile π-acceptor moiety for the catalytic activity and selectivity of p-tol1 in alkyne cyclotrimerization

Enhanced Catalytic Activity of Nickel Complexes of an Adaptive Diphosphine–Benzophenone Ligand in Alkyne Cyclotrimerization

Adaptive ligands, which can adapt their coordination mode to the electronic structure of various catalytic intermediates, offer the potential to develop improved homogeneous catalysts in terms of activity and selectivity. 2,2′-Diphosphinobenzophenones have previously been shown to act as adaptive ligands, the central ketone moiety preferentially coordinating reduced metal centers. Herein, the utility of this scaffold in nickel-catalyzed alkyne cyclotrimerization is investigated. The complex [(p-tolL1)Ni(BPI)] (p-tolL1 = 2,2′-bis(di(para-tolyl)phosphino)-benzophenone; BPI = benzophenone imine) is an active catalyst in the [2 + 2 + 2] cyclotrimerization of terminal alkynes, selectively affording 1,2,4-substituted benzenes from terminal alkynes. In particular, this catalyst outperforms closely related bi- and tridentate phosphine-based Ni catalysts. This suggests a reaction pathway involving a hemilabile interaction of the C═O unit with the nickel center. This is further borne out by a comparative study of the observed resting states and DFT calculations

Enhanced Catalytic Activity of Nickel Complexes of an Adaptive Diphosphine–Benzophenone Ligand in Alkyne Cyclotrimerization

Adaptive ligands, which can adapt their coordination mode to the electronic structure of various catalytic intermediates, offer the potential to develop improved homogeneous catalysts in terms of activity and selectivity. 2,2′-Diphosphinobenzophenones have previously been shown to act as adaptive ligands, the central ketone moiety preferentially coordinating reduced metal centers. Herein, the utility of this scaffold in nickel-catalyzed alkyne cyclotrimerization is investigated. The complex [(p-tolL1)Ni(BPI)] (p-tolL1 = 2,2′-bis(di(para-tolyl)phosphino)-benzophenone; BPI = benzophenone imine) is an active catalyst in the [2 + 2 + 2] cyclotrimerization of terminal alkynes, selectively affording 1,2,4-substituted benzenes from terminal alkynes. In particular, this catalyst outperforms closely related bi- and tridentate phosphine-based Ni catalysts. This suggests a reaction pathway involving a hemilabile interaction of the C═O unit with the nickel center. This is further borne out by a comparative study of the observed resting states and DFT calculations

Nickel-Catalyzed Alkyne Cyclotrimerization Assisted by a Hemilabile Acceptor Ligand: A Computational Study

π-coordinating units incorporated in the supporting ligand of an organometallic complex may open up specific reactive pathways. The diphosphine ketone supported nickel complex [(p-tolL1)Ni(BPI)] (p-tol1; p-tolL1 = 2,2′-bis(di-p-tolylphosphino)benzophenone; BPI = benzophenone imine) has previously been shown to act as an active and selective alkyne cyclotrimerization catalyst. Herein, DFT calculations support an adaptive behavior of the ligand throughout the catalytic cycle, several elementary steps being assisted by coordination or decoordination of the C═O moiety. A comparison with related bi- and tridentate phosphine ligands reveals the key role of the hemilabile π-acceptor moiety for the catalytic activity and selectivity of p-tol1 in alkyne cyclotrimerization

Cooperative Si–H Addition to Side-On Ni(0)-Imine Complexes Forms Reactive Hydrosilazane Complexes

Activation of a Si–H bond is commonly a critical step in catalytic hydrosilylation reactions. Herein, we investigate the cooperative reactivity of Ni(0) centers bearing a side-bound imine ligand toward silanes. Such complexes activate a Si–H bond of diphenylsilane, resulting in formal hydrosilylation of the imine backbone, which acts as a hydride acceptor. The resulting hydrosilazane motif engages either in coordination to nickel via the Si–H bond, forming an 18-electron η2-Si–H complex, or oxidative addition to Ni to form 16-electron Ni(II) silyl/hydride complexes. DFT calculations suggest a cooperative activation of the silane via ligand-to-ligand hydride transfer. In addition, the silicon fragment readily exchanges with external hydrosilanes, showing that the Si–N bond can be reversibly cleaved under mild conditions

Versatile Coordination and C–C Coupling of Diphosphine-Tethered Imine Ligands with Ni(II) and Ni(0)

The coordination chemistry of a series of diphosphine-imine ligands (PCNP) to Ni is investigated, with the purpose of developing systems that present metal−ligand cooperativity. The ligands bind in versatile ways, adapting to the oxidation state and coordination environment of the metal center. Additionally, a dimeric derivative undergoes oxidative C−C coupling in the presence of CO, resulting in an unusual mixed valence Ni(II)/Ni(0) dinuclear complex

Versatile Coordination and C–C Coupling of Diphosphine-Tethered Imine Ligands with Ni(II) and Ni(0)

The coordination chemistry of a series of diphosphine-imine ligands (PCNP) to Ni is investigated, with the purpose of developing systems that present metal−ligand cooperativity. The ligands bind in versatile ways, adapting to the oxidation state and coordination environment of the metal center. Additionally, a dimeric derivative undergoes oxidative C−C coupling in the presence of CO, resulting in an unusual mixed valence Ni(II)/Ni(0) dinuclear complex

Cooperative Si–H Addition to Side-On Ni(0)-Imine Complexes Forms Reactive Hydrosilazane Complexes

Activation of a Si–H bond is commonly a critical step in catalytic hydrosilylation reactions. Herein, we investigate the cooperative reactivity of Ni(0) centers bearing a side-bound imine ligand toward silanes. Such complexes activate a Si–H bond of diphenylsilane, resulting in formal hydrosilylation of the imine backbone, which acts as a hydride acceptor. The resulting hydrosilazane motif engages either in coordination to nickel via the Si–H bond, forming an 18-electron η2-Si–H complex, or oxidative addition to Ni to form 16-electron Ni(II) silyl/hydride complexes. DFT calculations suggest a cooperative activation of the silane via ligand-to-ligand hydride transfer. In addition, the silicon fragment readily exchanges with external hydrosilanes, showing that the Si–N bond can be reversibly cleaved under mild conditions