Nicoletta Mantovani

2-Oxacyclopentylidene, 2-Oxacyclohexylidene, and 2-Oxacycloheptylidene Rhenium Complexes by Reaction of ω-Alkynols with the [{MeC(CH2PPh2)3}Re(CO)2]+ Auxiliary

Various β-, γ-, and δ-alkynols have been reacted with the 16e− fragment [(triphos)Re(CO)2]+ generated in situ by H2 elimination from [(triphos)Re(CO)2(η2-H2)]BF4 [triphos = MeC(CH2PPh2)3]. Irrespective of the length of the alkyl chain between the C≡C and OH functional groups in the ω-alkynol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)Re(CO)2{=CCH2CH2CH2O}]BF4 and [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)2{=CCH2CH2CH2CH2O}]BF4 and[(triphos)Re(CO)2{=CCH2CH2CH2CH(Me)O}]BF4, and the 2-oxacycloheptylidene complex [(triphos)Re(CO)2{=CCH2CH2- CH2CH2CH2O}]BF4. The latter compound contains a unprecedented seven-membered oxacarbene ring. The rhenium-assisted δ-alkynol to 2-oxacyloheptylidene rearrangement proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO)2{C=C(H)CH2CH2CH2CH2OH}]BF4, which has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single crystal of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4. The structure of this complex consists of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]+ cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly distorted octahedral environment.

Activation of 2-propyn-1-ols by the rhenium(I) fragment [{MeC(CH2PPh2)3}Re(CO)2]+. Synthesis and characterization of cationic Re(I) complexes containing unsaturated η1-carbon ligands

Abstract The [{MeC(CH2PPh2)3}Re(CO)2]+ auxiliary has been found to activate 1-ethynyl-1-cyclohexanol and 1-phenyl-2-propyn-1-ol yielding a variety of η1-carbon ligands, which includes hydroxyvinylidene, alkenylvinylidene, alkoxycarbene, η1-Csp-enynyl, secondary allenylidene, acyl, hydroxycarbene and alkoxycarbene groups. The reactivity of the allenylidene complex [{MeC(CH2PPh2)3}Re(CO)2{CCC(H)Ph}]+ toward water and methanol has been investigated.

Nucleophilic addition of phosphines to rhenium allenylidenes. Unprecedented double P–H bond activation to give an η1-P-phospha-1-butadienyl ligand

Tertiary phosphines PMe3−xPhx (x = 0–2) react with the rhenium allenylidene [(triphos)(CO)2Re(CCCPh2)]OTf (1) yielding γ-phosphonioalkynyl complexes [(triphos)(CO)2Re{CCCPh2(PMe3−xPhx)}]OTf [x = 0, (2); 1, (4); 2 (7)] which convert into the α-phosphonioallenyl derivatives [(triphos)(CO)2Re{C(PMe3−xPhx)CCPh2}]OTf [x = 0, (3); 1, (5); 2 (6)] at higher tempereature. The reactions of 1 with secondary, PHPh2, and primary, PH2CH2Fc (Fc = ferrocenyl), phosphines proceed with a similar mechanism, followed by single or double P–H bond cleavage. The γ-phosphonioalkynyl [(triphos)(CO)2Re{CCCPh2(PHPh2)}]OTf (9) and the α-phosphonioallenyl [(triphos)(CO)2Re{C(PHPh2)CCPh2}]OTf (10) have been intercepted by insitu NMR spectroscopy. On increasing the temperature, 10 undergoes a selective 1,3-P,C-H shift to give the α-phosphoniobutadienyl derivative [(triphos)(CO)2Re{C(PPh2)CHCPh2}]OTf (8). With the primary phosphine PH2CH2Fc, the initially formed α-phosphoniobutadienyl complex [(triphos)(CO)2Re{C(PHFc)CHCPh2}]OTf (11) transforms into the η1-P-phospha-1-butadienyl complex [(triphos)(CO)2Re{P(CH2Fc)CHCHCPh2}]OTf (12) upon heating at 50 °C.

1,3-Cycloaddition of pyrazole to the allenylidene ligand in [Re{CCCPh2}(CO)2{MeC(CH2PPh2)3}]+

Abstract The reaction of the allenylidene complex [Re{CCCPh 2 }(CO) 2 (triphos)]OTf ( 1 ) (triphos=MeC(CH 2 PPh 2 ) 3 ; OTf= − OSO 2 CF 3 ) with pyrazole gave the 1,2,3-diheterocyclization product [Re{CCHCPh 2 (N 2 C 3 H) 3 }(CO) 2 (triphos)]Y (Y=OTf, 2OTF ; Y=BPh 4 , 2BPh 4 ). The molecular structure of this complex was determined by a single-crystal X-ray analysis. Treatment of 2 with sodium methoxide gave the pyrazolyl-functionalized alkynyl derivative [Re{CCCPh 2 (N 2 C 3 H 3 )}(CO) 2 (triphos)] ( 3 ) via selective deprotonation of the vinylic hydrogen, followed by back opening of the metal-bound heterocycle. Protonation of 3 with triflic acid in dichloromethane re-generated 1 and free pyrazole. The overall result of this deprotonation/protonation sequence allowed us to propose a reliable mechanism for the formation of the 1,2,3-diheterocyclization product 2OTf .

Synthesis and chemistry of 2-oxacyclocarbene and 2-cyclovinyl ether ligands supported by the [{MeC(CH2PPh2)3}Re(CO)2]+ auxiliary

Abstract The rhenium(I) cyclovinyl ether complexes [(triphos)Re(CO)2{CCHCH2(CH2)nO}]BF4 [triphos=MeC(CH2PPh2)3; n=1, 2] have been synthesized through the reversible and regioselective deprotonation of the corresponding 2-oxacyclocarbene complexes [(triphos)Re(CO)2{CCH2CH2(CH2)nCH2O}]BF4 (n=1, 2). The structure of the octahedral 2-oxacyclohexylidene complex [(triphos)Re(CO)2(CCH2CH2CH2CH2O)]BF4 has been determined by a single-crystal X-ray diffraction analysis.

Synthesis, characterization, properties and structures of rhenium-(II), -(III), and -(V) complexes containing amino acids conjugated with a 2-aminothiazole ligand

The one-step reaction of KReO4 with benzoylhydrazine in the presence of concentrated HCl and PPh3 afforded [ReV(NNC(Ph)O)(PPh3)2Cl2] 1 which was converted with carbon monoxide into the dinitrogen Re(I) complex [ReN2(CO)2(PPh3)2Cl] 2 in good yield. A new class of ligands, of general formula HLn (n = 1–5), was obtained by conjugation of N-protected amino acids and benzoic acid with 2-aminothiazole. Complex 2 reacted with HLn to give neutral Re(II) chelate complexes [Re(Ln)(CO)(PPh3)2Cl] 5–9 (n = 1–5), by substitution of N2 and CO groups. The molecular structure of complex 9 was determined by X-ray diffraction. When reactions between [Re(NNC(Ph)O)(PPh3)2Cl2] 1 and HLn (n = 2, 5) were carried out in different stoichiometric ratios, neutral mono- and di-substituted Re(III) organodiazenido complexes [Re(NNCOPh)(L2,5)(PPh3)2Cl] 10, 11 and [Re(NNCOPh)(L5)2(PPh3)] 12 were obtained. In these complexes the organodiazenido Re–N–N moiety adopts a linear conformation, as has been authenticated by X-ray diffraction analysis for 11 and 12. Treatment of Re(I) dinitrogen precursors [ReN2(P)4Cl] (P = PMe2Ph, 3 and PMePh2, 4) with ligands resulted in interesting dinuclear oxo-(μ-oxo)-Re(V) species [Re2(O)3(Ln)2(P)2] (P = PMe2Ph, n = 1, 13; n = 2, 14; n = 4, 15. P = PMePh2, n = 2, 16). Suitable crystals for an X-ray analysis have been obtained for complex 14. The structure represents one of the few cases where, for steric reasons, the Re–O–Re bridging unit is not linear but rather bent. All the compounds have been characterized by elemental analyses, IR and NMR spectroscopy. The Re(II) complexes 5–7 and 9 were further characterized by electrochemical measurements.