Linear Metal−Metal-Bonded Tetranuclear M−Mo−Mo−M Complexes (M = Ir and Rh):  Oxidative Metal−Metal Bond Formation in a Tetrametallic System and 1,4-Addition Reaction of Alkyl Halides

Abstract

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism.

Group 6 Complexes with Iron and Zinc Heterometals: Understanding the Structural, Spectroscopic, and Electrochemical Properties of a Complete Series of MM···M′ Compounds

“…The compounds discussed here are Cr 2 (dpa) 4 (1), Mo 2 (dpa) 4 (2), W 2 (dpa) 4 (3), CrCrFe(dpa) 4 Cl 2 (4), MoMoFe(dpa) 4 Cl 2 (5), WWFe(dpa) 4 Cl 2 (6), CrCrZn(dpa) 4 Cl 2 (7), [Cr 2 (dpa) 4 ]-(ZnCl 2 ) 2 (8), and [W 2 (dpa) 4 ]ZnCl 2 (9). Compound 6 is the first of these linear heterotrimetallic molecules to be reported Received: April 5, 2011 ABSTRACT: Binuclear quadruply bonded complexes Cr 2 (dpa) 4 (1, dpa = 2,2 0 -dipyridylamide), Mo 2 (dpa) 4 (2), and W 2 (dpa) 4 (3) react with anhydrous FeCl 2 , yielding heterometallic compounds CrCrFe(dpa) 4 Cl 2 (4), MoMoFe(dpa) 4 Cl 2 (5), and WWFe(dpa) 4 Cl 2 (6).…”

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

“…Similarly, Rh (or Ir) II −Mo II −Mo II −Rh (or Ir) II chain complexes 117 and 118 have been isolated following the same strategy, in which two Mo−M II single bonds were formed and the bond order of the Mo−Mo moiety has decreased to three (Scheme 29). 299 When M = Rh, the band observed at 389 cm −1 in the resonance Raman spectrum was assigned to the stretching vibration of the MoMo triple bond. 300 II single bonds, respectively.…”

“…An Ir I complex obtained from 111 reacted with MeI or CH 2 Cl 2 to afford the 1,4-oxidative addition product [Mo 2 Ir 2 (Me)­(I)­( t BuNC) 4 (pyphos) 4 ]­(Cl) 2 or [Mo 2 Ir 2 (CH 2 Cl)­(Cl)­( t BuNC) 4 (pyphos) 4 ]­(Cl) 2 containing Mo–Ir II single bonds, respectively. This reaction did not proceed with the Rh I analog …”

“…This reaction did not proceed with the Rh I analog. 299 The synthetic strategy developed with the quadruply bonded Mo 2 complex 111 was extended to its Cr II analog. 301 3.11.…”

“… Similarly, Rh (or Ir) II –Mo II –Mo II –Rh (or Ir) II chain complexes 117 and 118 have been isolated following the same strategy, in which two Mo–M II single bonds were formed and the bond order of the Mo–Mo moiety has decreased to three (Scheme ). When M = Rh, the band observed at 389 cm –1 in the resonance Raman spectrum was assigned to the stretching vibration of the MoMo triple bond . An Ir I complex obtained from 111 reacted with MeI or CH 2 Cl 2 to afford the 1,4-oxidative addition product [Mo 2 Ir 2 (Me)­(I)­( t BuNC) 4 (pyphos) 4 ]­(Cl) 2 or [Mo 2 Ir 2 (CH 2 Cl)­(Cl)­( t BuNC) 4 (pyphos) 4 ]­(Cl) 2 containing Mo–Ir II single bonds, respectively.…”