Monometallic Ni⁰ and Heterobimetallic Ni⁰/Au^I Complexes of Tripodal Phosphine Ligands: Characterization in Solution and in the Solid State and Catalysis

Abstract

The tridentate chelate nickel complexes [(CO)Ni{(PPh2 CH2 )3 CMe}] (2), [(CO)Ni{(PPh2 CH2 CH2 )3 SiMe}] (6), and [Ph3 PNi{(PPh2 CH2 CH2 )3 SiMe}] (7), as well as the bidentate complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 PPh2 }] (3) and the heterobimetallic complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 Ph2 PAuCl}] (4), have been synthesized and fully characterized in solution. All (1) H and (13) C NMR signal assignments are based on 2D-NMR methods. Single crystal X-ray structures have been obtained for all complexes. Their (31) P CP/MAS (cross polarization with magic angle spinning) NMR spectra have been recorded and the isotropic lines identified. The signals were assigned with the help of their chemical shift anisotropy (CSA) data. All complexes have been tested regarding their catalytic activity for the cyclotrimerization of phenylacetylene. Whereas complexes 2-4 display low catalytic activity, complex 7 leads to quantitative conversion of the substrate within four hours and is highly selective throughout the catalytic reaction.

Structures and Dynamics of Secondary and Tertiary Alkylphosphine Oxides Adsorbed on Silica

“…[31] For 1-3,( EtO) 2 PHO was reacted with the corresponding Grignard reagentsB rMg(CH 2 ) x CH=CH 2 (x = 4-6) that were obtained from the commercially availableb romoalkenes. The diphosphine dioxides 4 and 5 were synthesized by deprotonating 3 with NaH, followed by reaction with Br(CH 2 ) 14 Br and Br(CH 2 ) 8 Br,r espectively. [31]…”

“…Indeed,t he 31 Pw ideline and MAS spectra ( Figure 9) of 4a show that the CSA is only reduced, but not averaged out entirely.T he size of the molecule andt he long alkyl chains are not expected to slow the motion of an adsorbed species because it has been demonstrated earlier that paraffin, cyclododecane, or metallocenes with cycloalkyl substituents are highly mobile on silica and other surfaces. [13][14][15][16] Upon adsorption of 4 to form 4a all CSA parameters and the span of the signal are changed significantly,t he latter by nearly 100 ppm (Table2). Therefore, it can be concluded that both P=Og roups in the molecule are interacting equallyw ith the surfaceo fs ilica, but they actually do impedee ach other's mobility to some extent.…”

“…Encouraged by the meaningful results obtained with 1 Hw ideline NMR of adsorbed metallocenes [12][13][14][15][16] andm obile species in polymers [50] we probed 4 and 4a with this technique. The proton wideline spectrum of 4 shows as ignal that is broadened by large homonuclear dipolar interactions [17][18][19] and spans from about À110ppm to + 120 ppm, with ah alfwidth of ca.…”

“…[8] Early research in our group resulted in a study of paramagnetic chromocenes in polycrystalline and adsorbed form, [9,10] while Oprunenkoa nd Günther investigated biphenylene chromium tricarbonyl complexes. [11] Later,w e studied diverse diamagnetic and paramagnetic metallocenes and demonstrated that they can be adsorbed as solids on amorphous high surface area silica gel [12][13][14][15] and on various carbon supports. [16] In all the cases of successful solid/solid adsorption described in the literature, [6,7,9,[11][12][13][14][15][16] unique solid-state NMR [17][18][19][20] features were found due to the high translational mobilities of the adsorbate molecules on the surfaces.…”

“…Therefore, the anisotropic interactions dominating the signal shapes of crystalline solids, [17][18][19][20] dipolar and quadrupolar interactions, as well as the Chemical Shift Anisotropy (CSA) [17,18] of the signals of the adsorbeds pecies, are averaged out. [6,7,9,[11][12][13][14][15][16] Signals with larger residual linewidths, but devoid of rotational sidebands, result. The broader isotropic lines are ac onsequence of the less uniform surroundings of the nuclei on the support surfaces, as compared to their environment in asingle crystal.…”