Dichlorobis(triphenylphosphine)nickel(II) explained

Dichlorobis(triphenylphosphine)nickel(II) refers to a pair of metal phosphine complexes with the formula NiCl₂[P(C₆H₅)₃]₂. The compound exists as two isomers, a paramagnetic dark blue solid and a diamagnetic red solid. These complexes function as catalysts for organic synthesis.^[1]

Synthesis and structure

The blue isomer is prepared by treating hydrated nickel chloride with triphenylphosphine in alcohols or glacial acetic acid:

NiCl₂•6H₂O + 2 PPh₃ → NiCl₂(PPh₃)₂ + 6 H₂OWhen allowed to crystallise from chlorinated solvents, the tetrahedral isomer converts to the square planar isomer.

The square planar form is red and diamagnetic. The phosphine ligands are trans with respective Ni-P and Ni-Cl distances of 2.24 and 2.17 Å.^{[2] [3]} The blue form is paramagnetic and features tetrahedral Ni(II) centers. In this isomer, the Ni-P and Ni-Cl distances are elongated at 2.32 and 2.21 Å.^{[4] [5]}

As illustrated by the title complexes, tetrahedral and square planar isomers coexist in solutions of various four-coordinated nickel(II) complexes. Weak field ligands, as judged by the spectrochemical series, favor tetrahedral geometry and strong field ligands favor the square planar isomer. Both weak field (Cl⁻) and strong field (PPh₃) ligands comprise NiCl₂(PPh₃)₂, hence this compound is borderline between the two geometries. Steric effects also affect the equilibrium; larger ligands favoring the less crowded tetrahedral geometry.

Applications

The complex was first described by Walter Reppe who popularized its use in alkyne trimerisations and carbonylations.^[6] Dichlorobis(triphenylphosphine)nickel(II) is a catalyst in Suzuki reactions, although usually inferior in terms of activity.^[7]

See also

• Bis(triphenylphosphine)palladium(II) chloride
• Bis(triphenylphosphine)platinum(II) chloride
• Bis(tricyclohexylphosphine)nickel(II) chloride^[8]
• Dichloro(1,2-bis(diphenylphosphino)ethane)nickel

Notes and References

1. Montgomery, J. Science of Synthesis Georg Thiene Verlag KG, Vol. 1, p 11, CODEN: SSCYJ9
2. Batsanov . Andrei S. . Howard . Judith A. K. . 2001 . trans-Dichlorobis(triphenylphosphine)nickel(II) bis(dichloromethane) solvate: redetermination at 120 K . Acta Crystallogr E . 57 . 7 . 308–309 . 10.1107/S1600536801008741 . 2001AcCrE..57M.308B . 97381117 .
3. Corain . B. . Longato . B. . Angeletti . R. . Valle . G. . 1985 . trans:-[Dichlorobis(triphenylphosphine)nickel(II)]·(C₂H₄Cl₂)₂ a clathrate of the allogon of venanzi's tetrahedral complex . Inorg. Chim. Acta . 104 . 15–18 . 10.1016/S0020-1693(00)83780-9 .
4. Garton . G. . Henn . D. E. . Powell . H. M. . Venanzi . L. M. . Tetrahedral nickel(II) complexes and the factors determining their formation. Part V. The tetrahedral co-ordination of nickel in dichlorobistriphenylphosphinenickel . J. Chem. Soc. . 1963 . 1963 . 3625–3629 . 10.1039/JR9630003625 .
5. Brammer . L. . Stevens . E. D. . 1989 . Structure of dichlorobis(triphenylphosphine)nickel(II) . Acta Crystallogr C . 45 . 3. 400–403 . 10.1107/S0108270188011692. 1989AcCrC..45..400B .
6. Reppe . Walter . Sweckendiek . Walter . 1948 . Cyclisierende Polymerisation von Acetylen. III Benzol, Benzolderivate und hydroaromatische Verbindungen . Justus Liebigs Annalen der Chemie . 560 . 1. 104–16 . 10.1002/jlac.19485600104 .
7. 10.1039/c3cs35521g . Transition-metal-catalyzed Suzuki–Miyaura cross-coupling reactions: A Remarkable Advance from Palladium to Nickel Catalysts . 2013 . Han . Fu-She . Chemical Society Reviews . 42 . 12 . 5270–98 . 23460083.
8. Book: 10.1002/047084289X.rn01201 . Bis(tricyclohexylphosphine)dichloronickel . Encyclopedia of Reagents for Organic Synthesis . 2010 . Quasdorf . Kyle W. . Garg . Neil K. . 978-0-471-93623-7 .