3H‐Phosphaallenes Revisited: Facile Synthesis by Hydroalumination of Alkynylphosphines and β‐Elimination, Stability and Trapping of Transient Species by Coordination to Transition Metal Atoms

Abstract

A facile method for the efficient synthesis of 3H‐phosphaallenes, R−P=C=C(H)−R′, is presented, which comprises treatment of dialkynylphosphines with dialkylaluminium hydrides (hydroalumination) and elimination of aluminium alkynides from intermediate alkenyl‐alkynylphosphines. The stability of the phosphaallenes depends on steric shielding by the substituents at phosphorus (aryl or CH(SiMe3)2 groups). Only supermesityl compounds are persistent at room temperature in solution. This simple method starting with easily accessible dialkynylphosphines and commercially available aluminium hydrides (HAlEt2, HAliBu2) allows the generation of transient species, which were trapped by coordination to transition metals. The η1‐coordination via a P−W bond was observed for tungsten, while the side‐on coordination via the P=C bond resulted with platinum. Decomposition of the mesityl derivative yielded an unprecedented product, which may be formed by 1,3‐H shift to the P atom, hydrophosphination of the P=C bond of a second phosphaallene and formation of a P−P bond.

New Reactivity Patterns in 3H‐Phosphaallene Chemistry [Aryl‐P=C=C(H)‐tBu]: Hydroboration of the C=C Bond, Deprotonation and Trimerisation

“…The solid residue was treated with 10 mL of n-pentane. After filtration and removal of all volatiles from the filtrate compound 10 [2] was obtained as ac olorless oil (0.092 g, 92 %). 1 HNMR (400 MHz, C 6 D 6 ,3 00 K): d = 7.60 (d, 3 Reaction of 9a with chlorotrimethylsilane, synthesis of 11:As olution of 3H-3-tert-butylphosphaallene 3a (0.39 g, 1.09 mmol) in 10 mL of n-hexane was cooled to À78 8Ca nd treated with as olution of tert-butyllithium in n-pentane (570 mL, 1.9 m,1 .09 mmol).…”

“…[14] Compound 4 represents an unusual, asymmetricd imer with aP ÀP bond. [2] One Pa tom bears an alkynyl group, while the second one is boundt oa na lkenylg roup. The generation of 3H-phosphaallenes 3 by hydroalumination of dialkynylphosphines and elimination of aluminium alkynides [2] allows the generation of persistent( R = Mes*) and transients pecies [R = Trip,M es, CH(SiMe 3 ) 2 ], the latter could be trapped by coordination to transition metal atoms or showed as elective rearrangement reactiont oy ield compound 4 (Scheme 2).…”

“…[2] One Pa tom bears an alkynyl group, while the second one is boundt oa na lkenylg roup. The generation of 3H-phosphaallenes 3 by hydroalumination of dialkynylphosphines and elimination of aluminium alkynides [2] allows the generation of persistent( R = Mes*) and transients pecies [R = Trip,M es, CH(SiMe 3 ) 2 ], the latter could be trapped by coordination to transition metal atoms or showed as elective rearrangement reactiont oy ield compound 4 (Scheme 2). Ph-P=C=C(H)-tBu (3b)w ith the relatively smallPhg roup attached to Pi sa ccessible on as imilar route (Scheme6)a nd was identified by its characteristic 31 PNMR shift of d = 64.6.…”

“…Phosphaallenes, R-P=C=CR' 2 ,f orm af ascinating class of compounds. [1,2] They have cumulated P=Ca nd C=Cd ouble bonds, are highly reactive and only isolable with bulky substituents R such as Mes* (2,4,6-tBu 3 C 6 H 2 )t op reventd ecomposition. They were generated for the first time about4 0yearsa go by the seminalw ork of Yoshifuji [3,4] and further studied by the groups of Appel [5,6] andM ärkl.…”

Aryl-substituted Triarsiranes: Synthesis and Reactivity

“…Pure DipAsCl 2 (1b) was obtained by using Dip 2 Mg (obtained from DipMgBr and an excess of 1,4-dioxane) in the transmetalation with two equivalents AsCl 3 . [19] In a next step 1a and 1b were reduced using a mixture of PMe 3 and Zn powder in THF at ambient temperature and after removal of the solvent, extraction of the residue with n-hexane and concentration to incipient crystallization, the cyclotriarsanes (AsTip) 3 (2a) and (AsDip) 3 (2b) were obtained as colorless crystalline solids in 65% and 79% yield, respectively (Scheme 2).…”