Mono- and Dinuclear Rhodium(I) and Rhodium(III) Complexes with the Bulky Phosphine 2,6-Me₂C₆H₃CH₂CH₂PtBu₂, Including the First Structurally Characterized Cis-Configurated Dicarbonyl Compound,cis-[RhCl(CO)₂(PR₃)]

Abstract

The bulky functionalized phosphine 2,6-Me 2 C 6 H 3 CH 2 CH 2 PtBu 2 (3) was prepared in a stepwise fashion from the Grignard reagent 2,6-Me 2 C 6 H 3 CH 2 CH 2 MgCl, tBuPCl 2 , and tBuLi. Phosphine 3 reacts with the olefin compounds [RhCl(C 2 H 4 ) 2 ] 2 and [RhCl(C 8 H 14 ) 2 ] 2 to give the substitution products [RhCl(olefin)(3)] 2 (8, 9), of which 9 (olefin ) C 2 H 4 ) has been characterized crystallographically. While 9 is rather inert toward 3, it reacts with 3 under a hydrogen atmosphere to give the dihydrido complex [RhH 2 Cl(3) 2 ] (11) via the dimer [RhH 2 -Cl(3)] 2 (10) as an intermediate. In the presence of ethene, 11 is reconverted to 9. The reaction of 8 (olefin ) C 8 H 14 ) with the phosphonium salt 3‚HCl affords a mixture of [RhHCl 2 (3)] 2 (12) and 3, which upon warming at 60 °C produces [RhHCl 2 (3) 2 ] (13). The attempted separation of 12 by column chromatography on Al 2 O 3 led unexpectedly to the formation of the novel half-sandwich-type compound [(η 6 -2,6-Me 2 C 6 H 3 CH 2 CH 2 PtBu 2 -κP)RhCl] (14). Treatment of either 8 or 14 with CO gives cis-[RhCl(CO) 2 ( 3)] ( 15), which represents the first structurally characterized dicarbonyl complex with the CO ligands in a cis disposition. In the absence of carbon monoxide, 15 is rather labile and readily converted to [RhCl(CO)(3)] 2 (16). The reaction of 9 with HCl affords the dinuclear ethylrhodium(III) compound 18, being built up by two 14-electron [RhCl 2 (C 2 H 5 )(3)] units. These units are linked by two bridging chlorides which are unsymmetrically situated between the two metal centers. Compound 18 reacts with CO to give 15 and with 3 to give 13, presumably in both cases via [RhHCl 2 -(C 2 H 4 )(3)] as an intermediate. The half-sandwich-type complexes [(η 6 -2,6-Me 2 C 6 H 3 CH 2 -CH 2 PtBu 2 -κP)Rh(olefin)]PF 6 (20, 21), obtained from [Rh(acetone) 2 (C 8 H 14 ) 2 ]PF 6 as the precursor, react in acetone in the presence of H 2 to give [RhH 2 (acetone) 3 (3)]PF 6 (22), which upon addition of diethyl ether generates the dihydride [(η 6 -2,6-Me 2 C 6 H 3 CH 2 CH 2 PtBu 2 -κP)-RhH 2 ]PF 6 (23). Compound 23 is a suitable starting material for the preparation of compounds having the general composition [(η 6 -2,6-Me 2 C 6 H 3 CH 2 CH 2 PtBu 2 -κP)Rh(L)]PF 6 , where L is acetone, CH 2 dCHR (R ) tBu, Ph), PhCtCH, and CO, respectively.

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

“…This trend is also observed for the 1 J RhC coupling constants of carbonyl complexes with phosphine ligands [58–59]. Consequently, the signal at 186.3 ppm can be assigned to the trans -CO ligand and that at 183.2 ppm to the cis -CO ligand (relative to NHC).…”

On the P‐Coordinating Limit of NHC–Phosphenium Cations toward RhI Centers

“…[b] Experimentally obtained from reference [21]. and phosphinites subsequences a (R = Ph) and b (R = OEt) thus alternate perfectly in the main charge sequence q = 0, + 1, and + 2 for 9, 10, and 11, respectively, thus showing that the electron-withdrawing effect of substituting an ethoxy group (R = OEt) for a phenyl group (R = Ph) is much weaker (0.3 < ñ CO = < 5.5 cm À1 ) that the effect of adding a positive charge through a methylium cation (14.3 < ñ CO = < 31.3 cm À1 ).…”

Solvent‐Dependent Interconversions between RhI, RhII, and RhIII Complexes of an Aryl–Monophosphine Ligand

“…The rhodium-monophosphine system is based on the ligand a 2 -(diisopropylphosphino)isodurene (ligand 1, Scheme 1a), which was previously reported by our group in the context of cyclometalation by neutral Pt II complexes. [6,7] Similar cyclometalation was also found to occur upon reaction of ligand 1 with the cationic Rh I precursor [RhA C H T U N G T R E N N U N G (coe) 2 -A C H T U N G T R E N N U N G (acetone) 2 ]BF 4 (coe = cyclooctene). However, in contrast to the Pt II system, the present cyclometalation reaction was found to be highly reversible, resulting in the interesting valence interconversions described in this work.…”

“…This behavior of the cationic monophosphine-rhodium system described here stems from stabilization of the metal center by solvent molecules and from the versatile nature of ligand 1, which can serve as a s donor (via the phosphine), p donor (via the arene moiety), and substrate for C À H activation. [7] We believe that these findings should be kept in mind in the design and mechanistic evaluations of reactions promoted and catalyzed by rhodium complexes.…”

“…The response of the signals of the appropriate aromatic and aliphatic protons was detected by comparison (difference spectrum) with a control experiment in which a signalfree area was irradiated under the same conditions. CCDC-648207 (5 from acetone), CCDC-648208 (7), and CCDC-648209 (5 from THF) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.…”