Chelating ether–phosphine complexes of the cobalt group metals. Crystal structures of bis[benzylbis(2-ethoxyethyl)-phosphine]-bis(trifluoromethanesulfonato)cobalt(II) and -trichlororhodium(III)

Abstract

New Group 9 metal complexes have been prepared using the trifunctional ligand benzylbis(2-ethoxyethy1)phosphine (L). Reactions of this potentially hemilabile ligand with CoCI,, and CoCI,*6H20 with AgCF,SO,, have been studied, resulting in the isolation of [CoCI,L,] 1 and [CoL,(O,SCF,),]2 respectively. In the former complex L acts as a monodentate P-bonding ligand with the metal adopting a tetrahedral geometry, but in the latter it acts as an 0.P chelate. The crystal structure for 2 has been determined and shows the metal to have a distorted-octahedral geometry with trans ligands (P and 0) and trans triflates. The ,lP-{lH} NMR spectrum of 2 suggests the formation of a dimeric species in solution. Reactions of L with RhCI3.3H,O, [{RhCI(CO),},] and [{RhCl(cod)},] (cod = cycloocta-l,5-diene) resulted in the isolation of [RhCI,L,] 3, [RhCI(CO)L,] 4 and [RhCl(cod)L] 5 respectively, where L acts as a monodentate P-bonding ligand in 4 and 5.Complex 4 is shown to be trans by NMR studies. In 3 the ligand bonds as a monodentate phosphorus donor in one case and as a bidentate 0.P chelate in the other. The crystal structure of 3 has been determined and shows the metal to have a slightly distorted-octahedral mer arrangement with cis phosphorus donors. The fluxional nature of this complex has been monitored by variabletemperature ,lP-{'H) and lH NMR spectroscopy which shows that these ligands readily interchange at high temperatures. The iridium analogue of 5 has been prepared from [{lrCl(cod)},] resulting in the isolation of [IrCl(cod)L] 6 . The reaction of 3 with cyclohexene gave an unstable alkene complex 7 which could not be isolated, but was identified by variable-temperature 31P-{1H} NMR studies.

Coordination of a Hemilabile Pincer Ligand with an Olefinic Backbone to Mid-to-Late Transition Metals

“…Additionally, the average distance of 3.501 Å from cobalt to the centroid of the olefin supports this interpretation. Other metrical parameters compare well with those previously reported: the CoP distances in 2 (2.4236(18) and 2.4305(17) Å) are long compared to typical CoP distances (2.1–2.3 Å), − but a similar situation was observed before: 2.369(5) Å in [(Cy 3 P)­Co­(dmgH) 2 Cl] (dmgH = dimethyl­glyoximate), 2.418(1) Å in [(Ph 3 P)­Co­(dmgH) 2 (CH 3 )], 2.520(2) Å in [CoL 2 ­(O 3 SCF 3 ) 2 ] (L = P­(CH 2 Ph)­(CH 2 CH 2 OC 2 H 5 ) 2 , and 2.3666(14), 2.3731(15) Å in a Co­(II) tetrahedral complex supported by a PNP ligand, CH 3 N­(CH 2 ­CH 2 PPh 2 ) 2 . In the first three examples, the lengthening of CoP distances was attributed to the trans effect of other ligands.…”

Adaptive Behavior of a Ditopic Phosphine Ligand

“…Calculation (using the Eyring equation) of the free energy for the first process occurring above 25 °C gave Δ G ≠ = 15.5 kcal mol –1 at coalescence ( T c = 100 °C). This activation parameter is similar to that found for the related phosphine‐ether complex mer,cis ‐[RhCl 3 {PhCH 2 P(CH 2 CH 2 OEt) 2 } 2 ] (15.0 ± 0.1 kcal mol –1 ) . Determination of the energy barrier from the 1 H NMR spectra, led, within experimental error, to the same value (15.4 kcal mol –1 ; T c = 65 °C, based on the C H 2 CH 3 signals).…”

Ruthenium(II) Complexes Containing Optically Active Hemilabile P,N,O-Tridentate Ligands. Synthesis and Evaluation in Catalytic Asymmetric Transfer Hydrogenation of Acetophenone by Propan-2-ol

“…In recent years, the design of so-called hemilabile ligands containing one functional group strongly bound to a late transition metal and another coordinatively labile has been of considerable interest and developed by several groups. − The weakly bound functional group plays the role of an intramolecular solvent molecule assuring the stability of the complex and possibly improving its stoichiometric reactivity − or catalytic activity …”