Angela Marinetti

Electrophilic Terminal-Phosphinidene Complexes: Versatile Phosphorus Analogues of Singlet Carbenes

Electrophilic and nucleophilic terminal-phosphinidene complexes are compared in terms of electronic structures and reactivities. Various precursors of the unstable electrophilic species [R−P−M] (M=Cr, Mo, W(CO)5 and Fe(CO)4) are discussed. The addition reactions of the electrophilic phosphinidene complexes with Lewis bases, insertion reactions into O−H, N−H, and activated C−H bonds, and cycloaddition reactions with double and triple bonds are described, as well as some rearrangements and autocondensations. Various applications to the synthesis of new organophosphorus molecules are discussed and techniques available for demetallation are given.

Synthesis of Chiral Phosphetanes

Abstract Reactions of lithium phosphides with the mesylate, or the cyclic sulfate, of ( R , R )-2,4-pentanediol afford a general access to new chiral ligands based on the phosphetane moiety. Amongst others, the four membered ring analogue of Me-DuPHOS has been obtained by this method.

An investigation into a palladium catalyzed hydrosilylation of olefins

Abstract Hydrosilylations of styrene and cyclopentadiene are performed in the presence of phosphetane-palladium 1:1 and 2:1 complexes. An unprecedented inhibitory effect of the second phosphine ligand suggests a monophosphine-Pd catalyzed process which proceeds through four-coordinate intermediates.

Insertion of terminal alkynes into the phosphirene ring

Abstract In the presence of catalytic amounts of Pd(PPh 3 ) 4 , terminal alkynes readily insert into the ring of phosphirene P-W(CO) 5 complexes to give the corresponding phosphole complexes.

New chiral phosphetanes: Synthesis and use in the palladium-catalyzed allylic alkylation

The new chiral phosphetane—acetals 4a–d and 10a–d were synthesized and evaluated as coligands for the palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with sodium malonate. For each set of epimeric phosphetanes, the enantiomeric excesses are highly dependent on the relative configurations of the various chiral centers. The highest asymmetric induction was observed with phosphetane 4a. An X-ray crystal structure of the complex (allyl)PdCl(4a) is also reported.

Opening of phosphirane-tungsten-complexes by nucleophiles

Abstract The reactions of two phosphirane P-W(CO) 5 complexes with nitrogen, oxygen, phosphorus and sulphur nucleophiles have been studied. Except when the nucleophile is too bulky,the initial attack takes place at phosphorus. In this case, two main reaction paths have been observed: the first one is a ring opening giving a carbanion which may be protonated, or which can react with the W(CO) 5 group to yield a cyclic Fischer carbene complex. In the second reaction path, the whole carbon-carbon unit of the three-membered ring is lost and the final products formally result from the addition of the nucleophile onto the phosphinidene unit [RP→W(CO) 5 ]. Nitrogen and oxygen nucleophiles tend to follow the first path, whereas phosphorus and sulphur nucleophiles tend to follow the second one.

The ene reaction of phosphaalkynes with pentacarbocyltungsten complexes of phosphaalkenes

The W(CO) 5 -phosphaalkene complexes 9a, 6 , and 11 take part in ene reactions with the phosphaalkynes 1a–c to furnish the phosphinophosphaalkenes 10a–c and 12a , b containing the same metal fragment. In the reaction of 13 with 1a , the ene product 14 undergoes partial isomerization to the disphosphirane complext 15 . Ene reactions of the P -silyl, C -silyloxy-substituted phosphaalkene complex 19 with 1a–c follow the normal course of yield 20a–c .

Synthesis and α-alkylation of 1-menthylphosphetane sulfide

Abstract 1-Menthylphosphetane sulfide, 5, has been prepared from menthylphosphine and 1-bromo-3-chloropropane via the corresponding phosphetane-borane complex. The metalation-substitution reactions of both intracyclic α carbon atoms of 5 with benzyl and / or trimethylsilyl groups have been examined with regard to stereochemistry. The diastereoselectivity of these reactions is high enough to allow a preparative access to new chiral phosphetane sulfides.

Diastereoselective synthesis of α-silylphosphetanes. An approach to monodentate, PO chelating and trans-chelating chiral ligands

Abstract Optically pure α-silylphosphetanes have been prepared through stereoselective metallation-silylation reactions of the P-menthylphosphetane oxide 1. Bridging of two phosphetane units by means of bifunctional chlorosilanes leads to various bidentate ligands and, particularly, to the chiral, trans-chelating diphosphine 6b. Its square planar rhodium complex trans-Rh(CO)Cl(6b) has been structurally characterized.

Catalytic hydrogenation of the phosphorus–carbon double bond in phosphaalkene complexes

Abstract The catalytic transformations of phosphaalkene P–W(CO)5 complexes under H2 pressure in the presence of rhodium catalysts have been studied. In the presence of the cationic complex Rh(diphos)+ isomerization of phosphaalkene into secondary vinylphosphine complexes is greatly favoured. On the other hand, in the presence of the covalent Rh(diphos)Cl complex hydrogenation of the P=C double bond is greatly predominant. Experiments with deuterium in place of hydrogen indicated that there is clean cis addition of H2 or D2 to the double bond. No scrambling between tungsten and rhodium is observed in the postulated transient η1-P, η2-PC 4-electron phosphaalkene complexes.