Mark J. M. Vlaar

Carbene‐Like Chemistry of Phosphinidene Complexes − Reactions, Applications, and Mechanistic Insights

The versatile carbene-like chemistry of electrophilic phosphinidene complexes (R−P=MLn) with C=C, C≡C, C=X, and C≡X (X = N, O, S, Si, and P) bonds and aromatics is discussed.

INSERTION REACTIONS INTO PALLADIUM-CARBON BONDS OF COMPLEXES CONTAINING NEW RIGID BIDENTATE NITROGEN LIGANDS

Abstract The neutral complexes Pd(Me)Cl(DPIA) (3) and Pd(Me)Cl(DQIA) (4), containing the novel rigid bidentate nitrogen ligands (5,6-dihydro-[1]pyrindin-7-ylidene)-isopropylamine (DPIA) and (6,7-dihydro-5H-quinolin-8-ylidene)-isopropylamine (DQIA), respectively, have been synthesized. Complexes 3 and 4 react quantitatively with CO to give the neutral acylpalladium complexes Pd(C(O)Me)Cl(DPIA) (6) and Pd(C(O)Me)Cl(DQIA) (7), respectively. Complexes 3, 4, 6, and 7, which were present as mixtures of the cis and trans isomers, were fully characterized, and in the case of complexes 6 and 7 single crystal X-ray structures have been determined. The molecular structure of 6 and 7 show a square planar geometry with the α-diimine ligands coordinated in a bidentate fashion with comparable bite angles of about 78°. The acylpalladium complexes 6, 7, and Pd(C(O)Me)Cl(iPr–PyCa) (5), containing the nitrogen ligand 2-(N-2-propanecarbaldimino)pyridine (iPr–PyCa), which is the flexible analogue of DPIA and DQIA, react with norbornadiene to yield the ionic alkyl complexes [Pd(C7H8C(O)Me)(DPIA)]Cl (9a), [Pd(C7H8C(O)Me)(DQIA)]Cl (10a), and [Pd(C7H8C(O)Me)(iPr–PyCa)]Cl (8a), respectively. Interestingly, the nature of the α-diimine ligand influences the reaction rate of the norbornadiene insertion in the order N–N=DQIA≪iPr–PyCa

Addition of a phosphinidene complex to C=N bonds: P-ylides, azaphosphiridines, and 1,3-dipolar cycloadditions.

The terminal phosphinidene complex PhPW(CO)5 adds to the imine bond of PhHC=N-Ph to give 3-membered ring azaphosphiridines, which undergo ring-expansion with an additional imine to yield a set of four isomeric five-membered ring diazaphospholanes. Treatment with the diimines PhHC=N-(CH2)n-N=CHPh (n=2,3,4) results instead-in all three cases-in only a single isomer of the (CH2)n bridged diazaphospholane. For n=2 or 3, this aminal group is easily hydrolyzed to afford new 6- and 7-membered ring heterocycles. No intermediate azaphosphiridine complex is observed during the addition reaction to the diimines. B3LYP/6-31G* calculations on an unsubstituted, uncomplexed system suggest that the initially formed P,N-ylide of the H2C=N-(CH)2-N=CH2 diimine both kinetically and thermodynamically favors an intramolecular 1,3-dipolar cycloaddition over an imine insertion into the CPN ring of an intermediate azaphosphiridine. Single-crystal X-ray structures for the (CH2)2-bridged azaphospholane complex and the HCl adduct of the 7-membered hydrolysis product are presented.

Reaction of a complexed phosphinidene with 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene.

The terminal phosphinidene complex PhPW(CO)5 reacts with 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene to give two unexpected multicyclic organophosphorus compounds. One of them results from an initial 1,2-addition, followed by an intramolecular rearrangement. B3LYP/6-31G* calculations on simplified parent systems suggest that the reaction follows a unique concerted reaction pathway. The second, and major, product is a tetraphosphaquadricyclane derivative, which presumably results from an intramolecular [2+2] cycloaddition of an intermediate tetraphosphanorbornadiene complex. Single-crystal X-ray structures are presented for both products.

Metal-template-directed synthesis of diphosphorus compounds through intramolecular phosphinidene additions

Heating the nonchelating cis-bis-7-phosphanorbornadiene-[Mo(CO)4] complex (13) results in the thermal decomposition of one of the 7-phosphanorbornadiene groups. The phosphinidene thus generated adds intramolecularly to a C=C bond of the other ligand to give the novel diphosphorus complex 14. This reaction constitutes a metal-template-directed synthesis. Likewise, the intramolecular phosphinidene addition to the C=C bond of a Mo-phospholene ligand affords the diphos complex 18. Its crystal structure exhibits an extremely small P-Mo-P bite-angle for a five-membered chelate ring. The similar intramolecular 1,2-addition to a C=C bond of a phosphole ligand gives a highly strained, unstable intermediate product. Scission of its P-Mo bond generates a free coordination site, which is then occupied by either CO or a phosphole to yield complexes 22 and 23, respectively. The analogous intermolecular addition of [PhPW(CO)5] to a [phosphole-W(CO)5] complex gives the di-[W(CO)5] complexed adduct 28. The directing effect of the metal on the intra- and intermolecular additions is discussed.

Phosphinidene reactivity toward unsaturated phosphorus heterocycles

The transient electrophilic phosphinidene complex PhPW(CO) 5 reacts in the presence of CuCl at room temperature with phospholene 2 and phospholes 4a – c to give the corresponding W(CO) 5 complexed products 3 and 5a – c . The intermediate phosphoranylidene phosphine complexes, formed, from the addition of PhPW(CO) 5 to the phosphorus atom of the substrates, are characterized by NMR spectroscopy and by a single crystal X-ray structure determination for the one generated from phospholene 2 . This intermediate 8 is a CuCl-complexed dimer, which speculatively results from dissociating the phosphole–CuCl tetramer on insertion of PhPW(CO) 5 into the P–Cu bonds. Reacting PhPW(CO) 5 with phospholene 2 at 110°C in the absence of CuCl gives besides the W(CO) 5 -complexed phospholene 3 also a bisphospholene–W(CO) 4 complex 13 . The formation of 13 is attributed to a ligand exchange reaction in the intermediate phosphinidene–phospholene adduct.

Structural properties of azaphosphirane and its W(CO)5 complex. A density functional study

Abstract Properties and ring opening reactions are investigated for azaphosphirane and its P -phenyl and W(CO) 5 complex using density functional theory (B3LYP). Azaphosphirane has a relatively small N-inversion barrier of 10.8 kcal mol −1 and a high 56.8 kcal mol −1 ‘turnstile’ P-inversion barrier. Its strain energy is 26.5 kcal mol −1 at G3(MP2). The PC bond is the weakest bond. Only 27.4 kcal mol −1 is needed to break it, which is half that needed for both the CN and PN bonds. This PC ring opening to the P , N -ylide is endothermic by 8.5 kcal mol −1 . P -phenyl substitution has little effect neither on the geometries nor on the energy of the ring opening. Complexation by W(CO) 5 leads to a tighter ring but the energy for breaking the PC bond still requires 27.8 kcal mol −1 . The resulting P , N -ylide is only 3.9 kcal mol −1 less stable than azaphosphirane. Cleaving either the CN or PN bond remain much more demanding processes. The calculations suggest that the reactivity of azaphosphirane may well have its origin in the readily accessible P , N -ylide. Its influence on the reaction of phosphinidenes with imines is discussed.

C−N Bond Insertion of a Complexed Phosphinidene into a Bis(imine) − A Novel 2,3‐Sigmatropic Shift

The electrophilic phosphinidene complex PhPW(CO)5 reacts with bis(imine) 5, possessing a single carbon spacer, to give the C−N insertion product 6. B3LYP/6-31G* calculations indicate that this process occurs by way of a 2,3-sigmatropic shift from the initially formed phosphane ylide. The alternative, 1,3-dipolar cycloaddition, followed by ring-opening of the bicyclic structure, can be ruled out since both steps are