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#### (R_{2}PC_{2}H_{4}PR_{2})Pd(0) Alkene and Ethyne Complexes

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##### Citation

Krause, J., Bonrath, W., & Pörschke, K.-R. (1992). (R_{2}PC_{2}H_{4}PR_{2})Pd(0)
Alkene and Ethyne Complexes.* Organometallics,* *11*(3),
1158-1167. doi:10.1021/om00039a023.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-47E1-4

##### Abstract

The palladium η

^{3}-allyl complex Pd(η^{3}-C_{3}H_{5})_{2}reacts with bidentate phosphanes^{i}Pr_{2}PC_{2}H_{4}P^{i}Pr_{2}and^{t}Bu_{2}PC_{2}H_{4}P^{t}Bu_{2}below -30-degrees-C to yield the light yellow, microcrystalline palladium(II) η^{1}-allyl compounds (R_{2}PC_{2}H_{4}PR_{2})Pd(η^{1}-C_{3}H_{5})_{2}(R =^{i}Pr (1),^{t}Bu (2)), which are stable to about -30-degrees-C. Above -30-degrees-C, the allyl substituents of 1 and 2 couple with reduction of palladium to form a mixture of (R_{2}PC_{2}H_{4}PR_{2})Pd^{0}1,5-hexadiene complexes. When this reaction is carried out in 1,5-hexadiene, the complexes (R_{2}PC_{2}H_{4}PR_{2})Pd(η^{2}-C_{6}H_{10}) (R =^{i}Pr (3),^{t}Bu (4)) are obtained in pure form. According to IR and NMR spectral data, the palladium atoms in 3 and 4 are coordinated at low temperature by the chelating diphosphane and (statically) by one of the two diene double bonds in a trigonal-planar geometry. At higher temperatures, a rapid exchange of the coordinated and uncoordinated double bonds occurs, passing through an intermediate with C_{2}symmetry. When suspensions of 1 in pentane and 2 in THF are warmed to 20-degrees-C, dinuclear diastereomers rac-/meso-{(R_{2}PC_{2}H_{4}PR_{2})Pd}_{2}(µ-η^{2}:η^{2}-C_{6}H_{10}) (R =^{i}Pr (5a,b),^{t}Bu (6a,b)) are obtained, which upon treatment with 1,5-hexadiene furnish mononuclear derivatives 3 and 4. Similarly, when 1 is reacted with 1,5-cyclooctadiene at 20-degrees-C, the mono- and dinuclear interconvertible complexes (^{i}Pr_{2}PC_{2}H_{4}P^{i}Pr_{2})Pd(η^{2}-C_{8}H_{12}) (7) and {(^{i}Pr_{2}PC_{2}H_{4}P^{i}Pr_{2})Pd}_{2}(µ-η^{2}:η^{2}-C_{8}H_{12}) (8) are produced. From the reaction of 1 and 2 with ethene, stable complexes (R_{2}PC_{2}H_{4}PR_{2})Pd(C_{2}H_{4}) (R =^{i}Pr (9), colorless; R =^{t}Bu (10), tan) result. The colorless mononuclear palladium(0) ethyne complexes (R_{2}PC_{2}H_{4}PR_{2})Pd(C_{2}H_{2}) (R =^{i}Pr (11),^{t}Bu (12)) may be prepared (a) by a displacement reaction of one of the isolated alkene complexes with ethyne, (b) by a reductive elimination and concomitant displacement reaction of the η^{1}-allyl complexes 1 and 2 with ethyne, or (c) in a one-pot synthesis from either Pd(η^{3}-C_{3}H_{5})_{2}or Pd(η^{3}-2-MeC_{3}H_{4})_{2}with^{i}Pr_{2}PC_{2}H_{4}P^{i}Pr_{2}or^{t}Bu_{2}PC_{2}H_{4}P^{t}Bu_{2}, respectively, and ethyne in excess. When the mononuclear ethyne complexes 11 and 12 are combined with an equimolar amount of the corresponding η^{1}-allyl complex 1 or 2, or the alkene complexes (especially the mononuclear 1,5-hexadiene (3, 4) or ethene (9, 10) derivatives), yellow dinuclear palladium(0) complexes {(R_{2}PC_{2}H_{4}PR_{2})Pd}_{2}(µ-C_{2}H_{2}) (R =^{i}Pr (13),^{t}Bu (14)) are produced, in which the ethyne ligand bridges two palladium atoms. All the (diphosphane)palladium(0) alkene (3-10) and ethyne complexes (11-14) exhibit a trigonal-planar coordination geometry about the palladium atom. Most of the compounds have been isolated in high yield.