Palladium-Assisted Regioselective Olefin Insertion into and β-Hydrogen Elimination of Hydrogen−Molybdenum and −Tungsten Bonds. Synthesis and Reactions of Heterodinuclear Hydrido Complexes of Palladium and Platinum with Molybdenum and Tungsten

Abstract

Smooth reVersible olefin insertion of ethyl acrylate, acrylonitrile, ethylene, dimethyl fumarate, and dimethyl maleate into MHCp(CO) 3 (M ) Mo (1a), W (1b)) has been catalyzed by Pd(PPh 3 ) 4 (4) or Pd(ethyl acrylate)(dppe) (8) at room temperature.Transition metal-hydride addition to olefins (so-called olefin insertion) is one of the most well-established, important, fundamental reactions in organometallic catalysis. 1 Such a process is frequently facile and reversible, as observed in transition-metal-catalyzed olefin isomerization 2 as well as in disproportionation of the alkyl ligands in dialkylplatinum(II) complexes. 3 However, for some transition-metal hydrides such as the molybdenum and tungsten hydrides MHCp(CO) 3 (M ) Mo (1a), W (1b)), olefin insertion did not take place, though alkynes with a strong electron-withdrawing group can insert. 4 Insertion and its reverse, -hydrogen elimination processes, generally require a coplanar transition state or intermediate consisting of a metal hydride and a CdC double bond. 5 We recently reported enhanced -hydrogen elimination in a heterodinuclear ethylplatinum-molybdenum complex, (dppe)EtPtMoCp(CO) 3 (2), giving the corresponding hydridoplatinummolybdenum complex (dppe)HPt-MoCp(CO) 3 (3a), which further reacts with alkynes having an electron-withdrawing group to cause facile reductive elimination to give MoHCp-(CO) 3 and Pt(alkyne)(dppe). 6 When a terminal alkyne is employed, the succeeding Markovnikov addition of MoHCp-(CO) 3 to the coordinated alkyne takes place to give the new heterodinuclear µ-alkenyl complexes (dppe)(µ-CH 2 dCR)PtMoCp(µ-CO)(CO). These facts prompted us to investigate the

Bimetallic Catalysis using Transition and Group 11 Metals: An Emerging Tool for CC Coupling and Other Reactions

“…Also involving transmetalation processes with changes in the oxidation states of the metals, the group of Komiya has reported the palladium-catalyzed regioselective insertion of olefins into MÀH bonds (M = Mo, W), [55] affording alkyl derivatives of Mo and W. Olefins such as ethyl acrylate, acrylonitrile or ethylene do not insert into the M À H bond but, in the presence of a Pd 0 catalyst, instant insertion takes place. The reaction is slower for M = W and for 1,2-disubstituted olefins, such as dimethyl fumarate and dimethyl maleate.…”

Aqueous Suzuki Coupling Reactions of Basic Nitrogen-Containing Substrates in the Absence of Added Base and Ligand: Observation of High Yields under Acidic Conditions

“…Structurally characterized palladacyclic aqua complexes have been found to be highly active Suzuki catalyst precursors at basic pH ranges below the p K a (10.9) of the Pd hydroxide species . However, it is likely that the aqua ligands in this reported example serve primarily as weakly bound ligands which easily dissociate and facilitate entry into the catalytic cycle.…”

Synthesis of heterodinuclear hydride complexes by oxidative addition of a transition-metal hydride to Pt(0) and Pd(0) complexes

“…However, when terminal alkenes such as methyl acrylate or acrylonitrile were employed, mononuclear branched alkylmolybdenum complexes 10 were observed (entries 3 and 4). We consider that these branched alkylmolybdenum complexes 10 are produced by a Markovnikov insertion of the alkene into the PdeH bond in 7a followed by the subsequent reductive elimination at Pd [14,30].…”

“…The last but not least methodology shown in Scheme 1 is the oxidative addition of mono-nuclear hydride complex to a zero-valent metal compound [13]. We previously communicated the oxidative addition of MHCp(CO) 3 (M ¼ Mo, W) to Pt(alkene)(dppe) (alkene ¼ styrene, ethyl acrylate) giving the corresponding heterodinuclear platinum hydride complex (dppe)HPteMCp(CO) 3 (M ¼ Mo, W) [14]. At the same time, Adams and coworkers also reported the preparation of ( t Bu 3 P)Pt(mWithout 1 H decoupling, a large PeH coupling ( 2 J PH ¼ 194 Hz) for the downfield resonance was observed in the 31 P NMR of 3a, while upfield resonance has no PeH coupling.…”