Crystal structures of four new iridium complexes, each containing a highly flexible carbodi-phos-phorane PCP pincer ligand

Compound [Ir(C8H12)(C51H45P4)]Cl2 or [Ir(cod)(CH(dppm)2-κ3P,C,P)]Cl2 (1a), was obtained from [IrCl(cod)]2 and the carbodi-phospho-rane (CDP) salt [CH(dppm)2]Cl [where cod = cyclo-octa-1,5-diene and dppm = bis-(di-phenyl-phosphino)methane]. Treatment of 1a with thallium(I) tri-fluoro-methane-sulfonate [Tl(OTf)] and subsequent crystallization gave complex [Ir(C8H12)(C51H45P4)](OTf)2·CH3CO2C2H5·CH2Cl2 or [Ir(cod)(CH(dppm)2-κ3P,C,P)](OTf)2·CH3CO2C2H5·CH2Cl2 (1b) [systematic name: (cyclo-octa-1,5-diene)(1,1,3,3,5,5,7,7-octa-phenyl-1,7-diphospha-3,5-di-phospho-niaheptan-4-yl)iridium(I) bis-(tri-fluoro-methane-sulfonate)-ethyl acetate-di-chloro-methane (1/1/1)]. This five-coordinate iridium(I) complex cation adopts a trigonal-bipyramidal geometry with the CDP carbon and one cod double bond in axial sites. Compound 1b represents the first example of a non-meridional coordination of the PCP pincer ligand [CH(dppm)2]+ with a P-Ir-P angle of 98.08 (2)°. Compound 2, [IrCl2H(C51H44P4)]·(CH3)2CO or [IrCl2H(C(dppm)2-κ3P,C,P)]·(CH3)2CO [systematic name: di-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,5λ5,7-triphospha-3-phospho-niahept-4-en-4-yl)iridium(III) acetone monosolvate], crystallizes as an acetone monosolvate. It is a six-coordinate IrIII coordination compound. Here, the PCP pincer ligand is coordinated in a meridional manner; one chlorido ligand is positioned trans to the carbon donor, the remaining two coordination sites being occupied by the second chlorido and a hydrido ligand trans to each other. Complex 3, [IrCl2H(C51H45P4)]Cl·5H2O or [IrCl2H(CH(dppm)2-κ3P,C,P)]Cl·5H2O [systematic name: di-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,7-diphospha-3,5-di-phospho-niaheptan-4-yl)iridium(III) chloride penta-hydrate], represents the conjugate CH acid of 2. The ligand [CH(dppm)2]+ is coordinated in a meridional manner. In the cationic six-coordinate IrIII complex 4, [IrClH(CO)(C51H44P4)]Cl·2CH3OH·H2O or [IrClH(CO)(C(dppm)2-κ3P,C,P)]Cl·2CH3OH·H2O [systematic name: carbonyl-chlorido-hydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,5λ5,7-triphospha-3-phos-pho-niahept-4-en-4-yl)iridium(III) chloride-methanol-water (1/2/1)], the chlorido ligand is found in the plane defined by the Ir center and the meridional PCP ligand; the H and CO ligands are positioned axially to this plane and trans to each other.

Reversible alkoxycarbene formation by C-H activation of ethers via discrete, isolable intermediates

A cationic iridium complex bearing a pendant ether ligand is shown to be in equilibrium with the corresponding dihydridoalkoxycarbene resulting from two consecutive C-H activations. Control of the conditions allows for the crystallographic characterization of all three complexes involved in the interconversion of ether and alkoxycarbene functionalities via sequential oxidative addition and α elimination.