109786-30-3Relevant articles and documents
Dihydride complexes of the cobalt and iron group metals: An investigation of structure and dynamic behavior
Heinekey,Van Roon, Mirjam
, p. 12134 - 12140 (2007/10/03)
The previously reported cationic dihydride complexes (PP3)MH2+ (M = Co, Rh and Ir; PP3 = P(CH2-CH2PPh2)3) have been prepared using improved synthetic methods. Variable-temperature 1H and 31P NMR spectra of these complexes reveal complex dynamic behavior. The hydride region 1H NMR spectra have been accurately simulated at all temperatures using a simple site permutation model after taking into consideration the opposite signs of the cis and trans H-P coupling constants. Partial deuteration of the hydride ligands in the rhodium and cobalt complexes is achieved by exposure to D2. In the partially deuterated samples, no evidence is found for a bound dihydrogen ligand, but the involvement of a dihydrogen species in the dynamic process which interchanges the two hydride positions remains a mechanistic possibility, as indicated by a kinetic isotope effect k(H)/k(D) = 1.3(1). The partially deuterated samples exhibit large and temperature-dependent isotope effects on the 1H NMR chemical shifts observed for the hydride resonances, which are attributed to isotopic perturbation of resonance. This arises from non-statistical occupation of the two different hydride sites and also leads to perturbation of the averaged H-P coupling constants. Similar observations have been made for the neutral iron complex (PP3)FeH2.
Syntheses and characterization of trigonal-bipyramidal rhodium(I) complexes of tris(2-(diphenylphosphino)ethyl)phosphine and determination of a spectroscopic trans-influence series by 31P{1H} NMR spectroscopy
Gambaro, Jeffrey J.,Hohman, William H.,Meek, Devon W.
, p. 4154 - 4159 (2008/10/08)
A series of low-spin, five-coordinate rhodium(I) complexes of the tripod ligand tris(2-(diphenylphosphino)ethyl)phosphine, PP3, were synthesized and characterized by elemental analyses, infrared spectra, and 31P{1H} NMR spectra. The complexes have trigonal-bipyramidal geometries in which the PP3 ligand occupies four of the five sites of C3v symmetry and the variable fifth ligand is monodentate. The 31P NMR spectral patterns are consistent with AMX3 and AKMX3 spin systems. The NMR spectra permit a determination of the trans influence of the fifth ligand on the rhodium-phosphorus apical coupling constant and the chemical shifts of the apical and equatorial phosphorus atoms of PP3.
Activation of 1-alkynes at 16-electron rhodium fragments. Some examples of thermodynamically favored rearrangements [M(π-HC≡CR)] → [M(H)(C≡CR)]
Bianchini, Claudio,Masi, Dante,Meli, Andrea,Peruzzini, Maurizio,Ramirez, José A.,Vacca, Alberto,Zanobini, Fabrizio
, p. 2179 - 2189 (2008/10/08)
The 16-electron fragments [(NP3)Rh]+ and [(PP3)Rh]+ react with 1-alkynes in THF at room temperature yielding Rh(III) cis hydride acetylide complexes of formula [(L)Rh(H)(C≡CR)]BPh4 [L = NP3, N-(CH2CH2PPh2)3; L = PP3, P(CH2CH2PPh2)3; R = H, n-C3H7, Ph, SiMe3, CH2OH, CHO, CO2H, CO2Et]. The crystal structure of the ethynyl derivative [(NP3)Rh(H)(C≡CH)]BPh4·1.5THF was determined by X-ray crystallography. The metal atom in the complex cation is octahedrally coordinated by the four donor atoms of NP3, a σ-bonded ethynyl group, and a hydride ligand. Crystal data: monoclinic, space group P21/n, a = 15.769 (3) A?, b = 32.458 (6) A?, c = 13.277 (6) A?; β = 105.21 (2)°, U = 6557 (1) A?3; Z = 4. The structure was solved by Patterson and Fourier techniques and refined to an R factor of 0.079 (Rw = 0.086) by using 3735 reflections with I > 3σ(I). Decreasing the temperature to -40°C does not change the nature of the products except for the reactions with HC≡CCO2Et. In this case, the π-alkyne adducts [(L)Rh-(π-HC≡CCO2Et)]BPh4 (L = NP3, PP3) are formed which are thermodynamically unstable in ambient temperature solutions to irreversibly give the corresponding hydride acetylide derivatives. The [Rh(π-HC≡CCO2Et)] → [Rh(H)(C≡CCO2Et)] rearrangement is preceded at lower temperature by a fluxional process on the 31P NMR time scale which involves the π-alkyne species. At low temperature, also propiolic acid, HC≡CCO2H, forms with the [(NP3)Rh]+ fragments a π-alkyne complex which converts, in ambient temperature solutions, into hydride acetylide and hydride carboxylate derivatives via two independent, almost equally favored pathways. Most of the hydride acetylide complexes of rhodium(III) react with excess NaBH4 in THF/ethanol yeilding Rh(I) σ-acetylides of formula [(L)Rh(C≡CR)] (R = n-C3H7, Ph, SiMe3, CH2OH, CO2Et, CHO). No interconversion between the NP3 hydride acetylide complexes and the parent vinylidenes [(NP3)Rh{C≡C(H)(R)}]BPh4 was observed.
Rhodium Complexes with Tripodal Polyphosphines as Excellent Precursors to Systems for the Activation of H-H and C-H Bonds
Bianchini, Claudio,Masi, Dante,Meli, Andrea,Peruzzini, Maurizio,Zanobini, Fabrizio
, p. 6411 - 6423 (2007/10/02)
The trigonal-bipyramidal (TBP) Rh(I) complexes (1) and (2) are protonated by strong acids to give, after addition of NaBPh4, the octahedral (OCT) cis-(chloride)hydrides BPh4 (3) and BPh4 (4) which, by reaction with NaBH4, yield the cis-dihydride BPh4 (6) and the monohydride (8), respectively .By treatment of 6 in acetone with an excess of NaBH4, the monohydride (7) is obtained.Protonation of 8 with HOSO2CF3 followed by addition of NaBPh4 affords the Rh(III) OCT complex BPh4 (9) for which the dichotomy η2-H2 versus cis-dihydride as a function of temperature has been demonstrated.Metathetical reactions of 2 with organolithium reagents give the ?-organyl complexes (11) and (12) which react with CO to give the corresponding ?-acyl derivatives (13) and (14).Decoordination of a phosphine arm of PP3 is a necessary step for the insertion reaction.The monohydride 7 undergoes electrophilic attack by MeSO3CF3 in THF to give CH4 and the ortho-metalated hydride RhH>(SO3CF3) (15) through the intramolecular activation of a phenyl C-H bond.The structure of the iodide derivative RhI>BPh4*C6H6*0.5CH3COCH3 (17a) was determined by X-ray crystallography.When the methylation of 7 is carried out in THF/benzene mixtures both 15 and the cis-(phenyl)hydride (SO3CF3) (22) are obtained.Decreasing the temperature or increasing the concentration of benzene favors intermolecular C-H activation over cyclometalation.Methylation of 7 in THF followed by addition of an excess of α,α,α-trifluorotoluene gives the cis-(trifluorotolyl)hydride (SO3CF3) (23) regardless of the temperature.The reductive elimination of the metalated phenyl from 15 is easily promoted by monodentate ligands such as hydride, halides, pseudohalides, pyridine, and CO to form Rh(I) TBP complexes of the formula n+ (n = 0, 1).OCT complexes of rhodium(III), in which the two additional coligands are disposed in mutually cis positions, are obtained by reacting solutions of 15 with a plethora of addenda such as H2, Cl2, and CS2.As a result, cis-dihydride, cis-dichloride, and η2-CS2 derivatives are obtained.Dihydrogen elimination from 9, protonation of 11, as well as methylation of 8 give (24) which exists in two isomeric forms.The + system neither intramolecularly inserts across a C-H bond from a phenyl ring nor intermolecularly activates aromatic C-H bonds.The factors that may be responsible for such a behavior are discussed.Compound 24 reacts with neutral or anionic monodentate ligands affording TBP Rh(I) complexes or oxidatively adds HSO3CF3 to give, after addition of NaBPh4, the OCT Rh(III) cis-(triflate)hydride BPh4 (25).
