Aryne Complexes of Zerovalent Metals of the Nickel Triad

Martin A. Bennett

doi:10.1071/CH10198

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Aryne Complexes of Zerovalent Metals of the Nickel Triad

Martin A. Bennett ^A

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^A Research School of Chemistry, Australian National University, ACT 0200, Australia. Email: bennett@rsc.anu.edu.au

Australian Journal of Chemistry 63(7) 1066-1075 https://doi.org/10.1071/CH10198
Submitted: 13 May 2010 Accepted: 9 June 2010 Published: 15 July 2010

Abstract

The chemistry of dihapto-aryne complexes of the zerovalent Group 10 metals of general formula [M(η²-aryne)L₂] (M = Ni, Pd, Pt; L = various tertiary phosphines) is reviewed, with emphasis on the highly reactive nickel(0) compounds (aryne = benzyne, C₆H₄; 4,5-difluorobenzyne, 4,5-C₆H₂F_2; 2,3-naphthalyne, 2,3-C₁₀H_6; L₂ = 2 PEt₃, 2 PⁱPr₃, 2 PCy₃, dcpe). These can be generated by alkali metal reduction of the appropriate (2-halogenoaryl)nickel(ii) halide precursors, such as [NiX(2-XC₆H₄)L₂], which in turn are accessible by oxidative addition of the 1,2-dihaloarene to nickel(0) precursors such as [Ni(1,5-COD)₂]. The X-ray structure of [Ni(η²-C₆H₄)(dcpe)] shows that this compound is a typical 16-electron Ni(0) (3d¹⁰) species in which benzyne acts as a 2π-electron donor. Several unusual organonickel compounds derived from [Ni(η²-4,5-C₆H₂F₂)(PEt₃)₂] have been isolated recently, including [Ni₂(μ-η²:η²-4,5-C₆H₂F₂)(PEt₃)₄], in which a 4π-electron donor 4,5-difluorobenzyne is located at right-angles to a pair of nickel atoms. Free benzyne can be intercepted by both [Ni(η²-C₂H₄)(dcpe)] and [Pt(η²-C₂H₄)(PPh₃)₂], but the resulting benzyne complexes rapidly insert benzyne to give the appropriate η¹:η¹-2,2′-biphenylyl complexes. [Pt(η²-C₆H₄)(PPh₃)₂] also undergoes rapid ortho-metallation to give [PtPh(2-C₆H₄PPh₂)(PPh₃)]. However, a trapping reaction has been used to make the first 1,4-benzdiyne complex, [{Ni(dcpe)₂}₂(μ-η²:η²-1,4-C₆H₂)] by treatment of the 4-fluorobenzyne complex [Ni(η²-4-FC₆H₃)(dcpe)] with LiTMP. The use of alkali metals in the preparation of the η²-benzyne complexes is avoided in a more recently developed procedure, which starts from (2-bromophenyl)boronic acid, and is based on Suzuki–Miyaura coupling. This procedure has made accessible for the first time an aryne complex of palladium(0), [Pd(η²-C₆H₄)(PCy₃)₂], and the labile nickel(0) complex [Ni(η²-C₆H₄)(PPh₃)₂]. The aryne-nickel(0) complexes Ni(η²-aryne)L₂ (L₂ = 2 PEt₃, dcpe) undergo sequential insertions into the aryne-metal bond with unsaturated molecules, such as CO, C₂F₄, substituted alkynes, substituted diynes, alkynylphosphines, and alkynyl thioethers, often with considerable regioselectivity. After the reductive elimination of two nickel-carbon σ-bonds, a variety of interesting polycyclic compounds can be obtained.

Acknowledgements

I thank Dr Steven Privér (School of Applied Sciences, RMIT University) for his assistance in preparing this paper.

References

Aryne Complexes of Zerovalent Metals of the Nickel Triad

Abstract

Acknowledgements

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