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1.
J Am Chem Soc ; 131(37): 13531-7, 2009 Sep 23.
Article in English | MEDLINE | ID: mdl-19702264

ABSTRACT

18-Electron nucleophilic, Schrock-type phosphinidene complexes 3 [Cp*(Xy-N[triple bond]C)Ir=PAr] (Ar = Mes*, Dmp, Mes) are capable of unprecedented [1 + 2]-cycloadditions with 1 equiv of isocyanide RNC (R = Xy, Ph) to give novel iridaphosphirane complexes [Cp*(Xy-N[triple bond]C) IrPAr C=NR]. Their structures were ascertained by X-ray diffraction. Density functional theory investigations on model structures revealed that the iridaphosphirane complexes are formed from the addition of the isocyanide to 16-electron species [Cp*Ir=PAr] forming first complex 3 that subsequently reacts with another isocyanide to give the products following a different pathway than its nitrogen analogue [Cp*Ir[triple bond]Nt-Bu] 1.


Subject(s)
Cyanides/chemistry , Imides/chemistry , Iridium/chemistry , Organometallic Compounds/chemistry , Phosphines/chemistry , Electrons , Quantum Theory
2.
J Am Chem Soc ; 131(19): 6666-7, 2009 May 20.
Article in English | MEDLINE | ID: mdl-19397260

ABSTRACT

Catalyst tuning by changing ligands is a well-established protocol in transition-metal chemistry. N-Heterocyclic carbenes (NHCs) and tertiary phosphines (R(3)P) are the ubiquitous ligand actors. Here we demonstrate that the relative sigma-donor/pi-acceptor ability of the NHC ligand itself can be influenced by a simple substituent-controlled conformational change, thereby directly impacting the reactivity of the transition-metal complex.


Subject(s)
Heterocyclic Compounds/chemistry , Methane/analogs & derivatives , Phosphines/chemistry , Ruthenium/chemistry , Catalysis , Methane/chemistry , Molecular Conformation
3.
J Am Chem Soc ; 131(10): 3741-51, 2009 Mar 18.
Article in English | MEDLINE | ID: mdl-19231812

ABSTRACT

The intramolecular substituent interchange in recently reported pentaorganosilicates is investigated by B3LYP calculations, which show excellent agreement with the experimental thermochemical data. Two types of ligand permutation are discerned (A and B), which both lead to racemization of the helical, spirocyclic anions. IRC calculations show that stereomutation A bifurcates into two enantiomeric reaction paths, which are inhibited by ortho substitution of the bidentate ligands. The other pathway (B) proceeds through a trigonal bipyramidal transition state with one bisequatorial bidentate ligand and is disfavored by increasing the pi-electron density of the ligand. A more electronegative fifth, monodentate substituent increases the barrier of pathway A and lowers that of pathway B, as in bis(biphenyl-2,2'-diyl)fluorosilicate, which is the first tetraorganofluorosilicate to be isolated and fully characterized. These concepts enabled us to design and synthesize methyl- and ethylbis([2]naphthylpyrrol-2,1'-diyl)silicate as Si-chiral pentaorganosilicates that are configurationally rigid at room temperature.

4.
Chemistry ; 14(5): 1499-507, 2008.
Article in English | MEDLINE | ID: mdl-18033719

ABSTRACT

1,2-Addition of transient W(CO)(5)-complexed phosphinidenes exo to hexamethyl Dewar benzene affords the novel 3-phosphatricyclo[3.2.0.0(2,4)]hept-6-ene complexes. The fused tricyclic phosphiranes are obtained as both the Z and the thermally less stable E isomers, the (31)P NMR chemical shifts of which differ by about 60 ppm. A computational investigation shows that the phosphorus pyramidalization and the presence of the gamma double bond are responsible for this effect. The semiquantitative results contribute to a more systematic understanding of the structural influences on (31)P chemical shieldings. The congested double bond of the Z isomer can be epoxidized with m-chloroperbenzoic acid (MCPBA) to afford a fused tetracyclic P,O bis-adduct.


Subject(s)
Algorithms , Heterocyclic Compounds, 3-Ring/chemistry , Organophosphorus Compounds/chemistry , Phosphorus/chemistry , Chlorobenzoates/chemistry , Epoxy Compounds/chemistry , Isomerism , Ligands , Magnetic Resonance Spectroscopy , Molecular Structure
5.
J Am Chem Soc ; 128(41): 13634-9, 2006 Oct 18.
Article in English | MEDLINE | ID: mdl-17031978

ABSTRACT

The exceptional stability of recently reported pentaorganosilicates is investigated by bond energy analyses. Experimental coupling constants are used to probe their electronic structure, entailing bonds with mixed ionic-covalent character. Our analyses reconfirm that the axial bonds are more prone to heterolytic cleavage than are the equatorial bonds. Aryl substituents provide substantial electronic stabilization by charge delocalization, but cause steric crowding due to ortho-hydrogen repulsion. In contrast, silicates with two ax,eq biaryl groups are not congested. The remaining substituent is confined to an equatorial site, where it is insensitive to elimination. These concepts adequately explain the experimentally observed stability trends and are valuable for designing other stable pentaorganosilicates.

6.
J Am Chem Soc ; 128(37): 12169-73, 2006 Sep 20.
Article in English | MEDLINE | ID: mdl-16967967

ABSTRACT

anti-W(CO)(5)-complexed 9-methyl-9-phosphabicyclo[6.1.0]nonatriene represents a covalently interlocked molecular bevel gear. Correlated movement of the phosphorus atom and the eight-membered ring by way of a "walk" rearrangement makes gear slippage impossible. The gearing motion is transferred to the four-toothed W(CO)(5) propeller connected to the rotating phosphorus atom, enabling a gearing ratio of 2:1 according to B3LYP and Car-Parrinello Molecular Dynamics calculations. Methyl substitution of the eight-membered ring tempers the gearing process, with the PMeW(CO)(5) entity passing the substituted carbon atom only at temperatures above 50 degrees C.


Subject(s)
Bridged Bicyclo Compounds/chemistry , Cycloparaffins/chemistry , Organophosphorus Compounds/chemistry , Tungsten Compounds/chemistry , Models, Molecular , Molecular Conformation , Thermodynamics
7.
Chemistry ; 12(16): 4333-40, 2006 May 24.
Article in English | MEDLINE | ID: mdl-16528775

ABSTRACT

Intramolecular phosphinidene addition to the C==C bond of Mo-complexed, seven-membered phosphorus heterocycles affords three novel [(diphos)Mo(CO)(4)] complexes (18-20). The three bidentate phosphorus baskets differ in the composition of the seven-membered ring: one of the phosphorus atoms is flanked by CH(2), NCH(3), or O. The unsaturated tetrahydrophosphepine precursors are synthesized by either ring-closing metathesis (C and N derivatives) or by a cyclization sequence (O derivative). The crystal structures of the nitrogen- (19) and oxygen-containing (20) baskets have relatively small P-Mo-P angles of 76.240(13) degrees and 77.626(12) degrees , respectively, and complex 20 has slightly shortened Mo--P bond lengths.


Subject(s)
Molybdenum/chemistry , Organometallic Compounds/chemistry , Phosphorus/chemistry , Molecular Conformation , Molecular Structure , Phosphines/chemistry
8.
J Am Chem Soc ; 127(48): 16985-99, 2005 Dec 07.
Article in English | MEDLINE | ID: mdl-16316245

ABSTRACT

The synthesis of a variety of benzophosphepine complexes [R = Ph, t-Bu, Me; ML(n )()= W(CO)(5), Mo(CO)(5), Cr(CO)(5), Mn(CO)(2)Cp] by two successive hydrophosphinations of 1,2-diethynylbenzene is discussed in detail. The first hydrophosphination step proceeds at ambient temperature without additional promoters, and subsequent addition of base allows full conversion to benzophosphepines. Novel benzeno-1,4-diphosphinanes were isolated as side products. The benzophosphepine complexes themselves serve as convenient phosphinidene precursors at elevated, substituent-dependent temperatures (>55 degrees C). Kinetic and computational analyses support the proposal that the phosphepine-phosphanorcaradiene isomerization is the rate-determining step. In the absence of substrate, addition of the transient phosphinidene to another benzophosphepine molecule is observed, and addition to 1,2-diethynylbenzene furnishes a delicate bidentate diphosphirene complex.

10.
Chemistry ; 11(23): 6982-93, 2005 Nov 18.
Article in English | MEDLINE | ID: mdl-16078293

ABSTRACT

Novel, highly stable, linear and branched mono- and diphospha[n]triangulanes were synthesized in high yields by the CuCl-catalyzed phosphinidene addition to spirocyclopropanated methylenecyclopropanes and bicyclopropylidenes. The effect of spirofusion on the electronic properties of these esthetically attractive phosphacycles is apparent from X-ray single crystal structure analyses, which reveals a tightening of the phosphirane ring on additional spirocyclopropanation, and from the NMR features that show deshielded chemical shifts for the ring-phosphorus and -carbon atoms. Steric factors play a role in the addition reaction when the substrate alkene carries a second sphere of spirocyclopropane rings and causes the formation of 2-phosphabicyclo[3.2.0]heptenes in small amounts. These by-products most probably result from addition of the [PhP(Cl)W(CO)(5)]-Cu-L (L=alkene or solvent) reagent to the spirocyclopropanated bicyclopropylidene to give an intermediate sigma-complex, which subsequently, facilitated by steric factors, undergoes a cyclopropylcarbinyl to cyclobutyl ring expansion followed by a [1,3]-sigmatropic shift.


Subject(s)
Organophosphorus Compounds/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , Spectrometry, Mass, Electrospray Ionization , Spectrophotometry, Infrared
11.
Chemistry ; 11(16): 4808-18, 2005 Aug 05.
Article in English | MEDLINE | ID: mdl-15954153

ABSTRACT

Reaction of the transient phosphinidene complexes R-P=W(CO)5 with N-substituted-diphenylketenimines leads unexpectedly to the novel 2-aminophosphindoles, as confirmed by an X-ray crystal structure determined for one of the derivatives. Experimental evidence for a methylene-azaphosphirane intermediate was found by using the iron-complexed phosphinidene iPr2N-P=Fe(CO)4, which affords the 2-aminophosphindole together with the novel methylene-2,3-dihydro-1H-benzo[1,3]azaphosphole. Analysis of the reaction pathways with DFT indicates that the initially formed methylene-azaphosphirane yields both phosphorus heterocycles by way of a [1,5]- or [1,3]-sigmatropic shift, respectively, followed by a H-shift. Strain underlies both rearrangements, which causes these remarkably selective conversions that can be tuned by changing the substituents.

12.
Chemistry ; 11(12): 3631-42, 2005 Jun 06.
Article in English | MEDLINE | ID: mdl-15812871

ABSTRACT

The synthesis of highly strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes, that is, complexes with 2-aza-1-phosphabicyclo[n.1.0]alkanes and -alkenes (n = 3-5), is explored by using intramolecular cycloaddition of an in situ generated electrophilic phosphinidene complex, [R(iPr)NP=Fe(CO)(4)], to its C=C- and C[triple chemical bond]C-containing R substituent. Saturated bicyclic complexes 7 a-c with n = 4-2 are remarkably stable, as illustrated by the X-ray crystal structure for 7 b (n=3), yet all readily undergo retroaddition to react with phenylacetylene. Shuttling of the phosphinidene iron complex between two equivalent C=C groups is demonstrated for a 1-butene-substituted 2-aza-1-phosphabicyclo[3.1.0]hexane by selective (1)H NMR magnetization transfer from the phosphirane protons to the olefinic protons. Even the more strained unsaturated bicycles 17 a,b (n = 4,3) are surprisingly stable as illustrated by the X-ray crystal structure for 17 a (n = 4), but the smaller phosphabicyclo[3.1.0]hex-5-ene (17 c, n = 2) dimerizes to tricyclic 19 with a unique ten-membered heterocyclic ring; an X-ray crystal structure is reported. Like their saturated analogues also the bicyclic phosphirenes readily undergo retroaddition as shown by the reaction of their phosphinidene iron moiety with phenylacetylene.


Subject(s)
Alkenes/chemical synthesis , Aza Compounds/chemical synthesis , Iron Compounds/chemistry , Organometallic Compounds/chemical synthesis , Phosphines/chemistry , Alkenes/chemistry , Aza Compounds/chemistry , Crystallography, X-Ray , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Models, Molecular , Molecular Structure , Organometallic Compounds/chemistry , Reference Standards
13.
J Am Chem Soc ; 127(16): 5800-1, 2005 Apr 27.
Article in English | MEDLINE | ID: mdl-15839673

ABSTRACT

Reaction of o-diethynylbenzene with transition metal-complexed primary phosphines gives in a single base-induced step stable phosphepine complexes as confirmed by X-ray data. At 75-80 degrees C these phosphepines undergo clean cheletropic elimination of naphthalene to give transient carbene-like phosphinidene complexes that can be trapped in high yield by alkenes, alkynes, and alcohols.

14.
Chemistry ; 10(21): 5332-7, 2004 Oct 25.
Article in English | MEDLINE | ID: mdl-15390134

ABSTRACT

Reaction of electrophilic phosphinidene complex [MePW(CO)5] with 1,6-methano-[10]annulene results in the sole formation of the isomeric C-C insertion products 6 c (main) and 6 d (minor). The single-crystal X-ray structure of the complexed 1,7-methano-3-phospha[11]annulene (6 c) shows a syn-W(CO)5 group at the exo bent phosphorus. The structure displays C-C bond alternation without bonding between the bridgehead carbon atoms. Density functional theory calculations indicate 6 c to result from a concerted disrotatory ring opening of an undetected tricyclic exo-syn phosphirane intermediate. The endo-anti phosphirane cannot undergo ring expansion, due to the high barrier that is associated with an intramolecular antara-antara retro Diels-Alder reaction. The stabilizing effect of transition-metal coordination is discussed.

15.
Chemistry ; 10(16): 4063-72, 2004 Aug 20.
Article in English | MEDLINE | ID: mdl-15316986

ABSTRACT

The properties of the 16-electron phosphinidene complex [CpRIr=PR] were investigated experimentally and theoretically. Density functional theory calculations show a preferred bent geometry for the model complex [CpIr=PH], in contrast to the linear structure of [CpIr=NH]. Dimerization to give [[CpIr=PH]2] and ligand addition to afford [Cp(L)Ir=PH] (L=PH3, CO) were calculated to give compounds that were energetically highly favorable, but which differed from the related imido complexes. Transient 16-electron phosphinidene complex [Cp*Ir=PAr] could not be detected experimentally. Dehydrohalogenation of [Cp*IrCl2(PH2Ar)] in CH2Cl2 at low temperatures resulted in the novel fused-ring systems 17 (Ar=Mes*) and 20 (Ar=Mes), with dimeric [[Cp*Ir=PAr]2] being the likely intermediate. Intramolecular C-H bond activation induced by steric factors is considered to be the driving force for the irreversible formation of 17 and 20. ONIOM calculations suggest this arises because of the large steric congestion in [[Cp*Ir=PAr]2], which forces it toward a more reactive planar structure that is apt to rearrange.


Subject(s)
Computer Simulation , Iridium/chemistry , Organometallic Compounds/chemistry , Phosphines/chemistry , Thermodynamics , Crystallography, X-Ray , Dimerization , Electrons , Models, Molecular , Molecular Conformation
16.
Chemistry ; 10(11): 2732-8, 2004 Jun 07.
Article in English | MEDLINE | ID: mdl-15195304

ABSTRACT

Reaction of an in situ generated phosphinidene complex [PhPW(CO)(5)] with the aromatic azulene and guaiazulene leads to unexpected 1,4-adducts of the seven-membered ring and to C--H bond insertion of the five-membered ring. A DFT analysis suggests that the reaction is initiated by formation of a eta(1)-complex between the phosphinidene and the five-membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn- and anti-1,2-adducts. These undergo pericyclic 1,7-sigmatropic rearrangements with remarkably low barriers to give 1,4-adducts, with an inverted configuration at the phosphorus center. An X-ray crystal structure is presented for one of the 1,4-adducts of guaiazulene. The other two eta(1)-complexes insert with modest barriers into a C--H bond of the five-membered ring.

19.
J Am Chem Soc ; 126(10): 3050-1, 2004 Mar 17.
Article in English | MEDLINE | ID: mdl-15012125

ABSTRACT

A highly strained, thermally stable (up to 150 degrees C) branched phospha[7]triangulane was synthesized from the second-generation bicyclopropylidene and transient phosphinidene [Ph-P=W(CO)5], followed by demetalation in refluxing xylene. Bulkier transient CuCl-alkene-complexed phosphinidene gave 2-phosphabicyclo-[3.2.0]hept-1(5)-ene as an additional product. The "outer sphere" spirocyclopropanes provide a stabilizing factor for both of these novel compounds.

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