Palladium-Catalyzed Hydrophosphorylation of Alkynes

Palladium(O) or readily reduced paUadium(II) complexes were the most efficient catalysts, giving higher yields than analogous Pt catalysts. The Markovnikov product was formed with high regioselectivity. In dialkynes, both C=C bonds could be hy-drophosphorylated, while the C=C double bond in a cyclohexenyl alkyne subshtuent did not react. With trimethylsilylacetylene, unusual anti-Markovnikov selectivity was observed. 

Addition of diaUcyl phosphites HP(0)(0R)2 to terminal alkynes led to the formation of bis-phosphonates in 47-90% yield. These products result from addition of two P-H bonds across the C=C triple bond. Interestingly, although diethyl phosphite gave good results, the isopropyl derivative gave lower yields, and only mono- 

P-H oxidative addition followed by alkyne insertion into a Pd-P bond gives the re-gio-isomeric alkenyl hydrides 15 and 16. Protonolysis with diaUcyl phosphite regenerates hydride 17 and gives alkenylphosphonate products 18 and 19. Insertion of alkene 18 into the Pd-H bond of 17 followed by reductive eUmination gives the bis-products, but alkene 19 does not react, presumably for steric reasons. P-Hydride elimination from 16 was invoked to explain formation of trace product 20. 

Stoichiometric reactions provided information on the mechanism of catalysis. Two equivalents of PH(0)Ph2 reacted with MlPEtj), (M = Pd, Pt) to give cis- 

NMR monitoring of the reaction of the palladium complex with 1-octyne suggested that the alkyne inserts into the Pd-H bond. Further heating produced a mixture of the two regioisomeric alkenylphosphine oxides, the anti-Markovnikov adduct being the favored product (54 46, 65% yield). 

---

R = n-CeHia, Ph, p-Tol, NC(CH2)a, HC=C(CH2)5, 3-HC=C-C6H4, 1-cyclohexenyl, SiMea Scheme 5-17 Palladium-catalyzed hydrophosphorylation of alkynes... 

Scheme 5-20 Proposed mechanism for palladium-catalyzed bis-hydrophosphorylation of alkynes...

Zhao Ch-Q, Han L-B, Goto M, Tanaka M (2001) Rhodium-catalyzed hydrophosphorylation of terminal alkynes leading to highly selective formation of (i )-afkenylphosphonates complete reversal of regioselectivity to the palladium-catalyzed counterpart. Angew Chem Int Ed 40 1929-1932... 

Hydrophosphorylation of alkenes and alkynes with phosphinic acid derivatives such as alkyl phosphinates [H2P(0)(0R)] and anilinium phosphinate [PhNH3 0P (0)H2] is successfully catalyzed by palladium complexes, in particular those ligated by xantphos and dppf [25]. Polymer-botmd palladium catalyst 11 has proved to catalyze the same reactions with phosphinic acid to give good yields, although the... 

Gulykina NS, Dolgina TM, Bondarenko GN, Beletskaya IP (2003) Hydrophosphorylation of terminal alkynes catalyzed by palladium. Russ J Org Chem 39 797-807... 

---