Structure of Tricarbonyl(diene)iron Complexes in Solution. Variable-Temperature Circular Dichroism of trans-μ-(2,3,5,6-Tetramethylidenebicyclo[2.2.2]octane)bis(tricarbonyliron) Complexes

Optically pure (?)-trans-μ-[(1R,2R,3S,4S,5S,6R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6,7-pentamethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 9 ), (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7S)-C,2,3,C-η:C,5,6,C-η-(7-methyl-2,3,5,6-tetramethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 10 ), and (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidene(7D)bicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 16 ) have been prepared. Their CD spectra were solvent- and concentration-independent, but temperature-dependent, in accord with the existence of equilibria between rapidly interconverting diastereoisomeric species which can be interpreted as arising from distortions of the tricarbonyl(diene)iron units from the C_s symmetry.     

Chiral exo-Alkylidenecyclopentanes from (1S,4R)-7,7-Dimethyl-1-vinylbicyclo[2.2.1]heptan-2-one

(1S,4R)-7,7-Dimethyl-1-vinylbicyclo[2.2.1]heptan-2-one oxime in the system (CF₃CO)₂O-CF₃COOH and (1S,4R)-1-(1,2-dibromoethyl)-7,7-dimethylbicyclo[2.2.1]heptan-2-one in the system MeONa-MeOH undergo fragmentation to give exo-alkylidenecyclopentane derivatives, (4R)-4-cyanomethyl-5,5-dimethyl-1-[(1E)-trifluoroacetoxyethylidene]cyclopentane and isomeric (4R)-4-carboxymethyl-1-[(1ZE)-2-methoxyethylidene]-5,5-dimethylcyclopentanes, respectively. The trifluoroacetate derivative undergoes unusual rearrangement, yielding an equilibrium mixture of two isomers with endo- and exocyclic double bond.     

Chemo- and Stereoselective Coordination of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene by d8- and d6-Metal Carbonyls. Diels-Alder reactivity of Dienes Perturbed by Remote Olefin Complexation

The endocyclic double bond C(2), C(3) in 5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene ( 1 ) can he coordinated selectively on its exo-face before complexation of the exocyclic s-cis-butadiene moiety. Irradiation of Ru₃(CO)₁₂ or Os₃(CO)₁₂ in the presence of 1 gave tetracarbonyl [(1R,2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene)]ruthenium ( 6 ) or -osmium ( 8 ). Similarly, irradiation of Cr(CO)₆ or W(CO)₆ in the presence of 1 gave pentacarbonyl[(1R, 2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]chromium (10) or -tungsten (11) . Irradiation of complexes 6 and 11 in the presence of 1 led to further CO substitution giving bed-tricarbonyl-ae-bis[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]ruthenium ( 7 ) and trans-tetracarbonyl[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo-[2.2.1]hept-2-ene)]tungsten (12) , respectively. The diosmacyclobutane derivative cis-m?-[(1R,3R,3S,4S)-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hepta-2,3-diyl)]bis(tetracarbonyl-osmium) (Os-Os) (9) wa also obtained. The Diels-Alder reactivity of the exocyclic s-cis-butadiene moiety in complexs 7 and 8 was found to be significantly higher than that of the free triene 1 .     

Ironcarbonyl Complexes of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene Derivatives. Synthesis of Substituted Tricarbonyl(ortho-quinodimethane)iron Complexes and 2-Indanones

The l-dimethoxymethyl-5,6-dimethyldene-7-oxabicyclo[2.2.1]hept-2-ene ( 9 ) has been prepared. On treatment with Fe₂(CO)₉, the endocyclic double bond C(2)?C(3) was coordinated first giving the corresponding exo-Fe(CO)₄ complex 10 . The latter reacted with Fe₂(CO)₉ and afforded cis-heptacarbonyl-μ-[1RS,2SR,3RS,4SR,5RS,6SR-2,3-η: C5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]diiron ( 11 ) as a major product. On heating, 11 underwent deoxygenation of the 7-oxabicyclo[2.2.1]heptene moiety yielding tricarbonyl[C,5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidenecyclohexa-1,3-diene)]iron ( 13 ). In MeOH, a concurrent, regioselective methoxycarbonylation was observed giving tricarbonyl[C,3,4,C-η-(methyl 5-(dimethoxymethyl)-3,4-dimethylidenecyclohexa-1,5-diene-1-carboxylate)]iron ( 14 ). Oxidative removal of the Fe(CO)₃ moiety in 13 and 14 did not afford the expected ortho-quinodimethane derivatives but led to CO insertions giving 2,3-dihydro-2-oxo-1Hindene-4-carbaldehyde ( 20 ) and methyl 7-formyl-2-3-dihydro-2-oxo-lH-indene-5-carboxylate ( 21 ), respectively.     

Synthesis of Polypropionate Fragments Containing Tertiary-Alcohol Moieties. Cross-aldolisations with lithium enolates of 7-oxabicyclo[2.2.1]heptan-2-one derivatives

The Diels-Alder adduct of 2,4-dimethylfuran to 1-cyanovinyl (1′R)-camphanate ((+)-(1R,2S,4R)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′R)-camphanate ((+)- 1 )) was converted into (+)-2,7-dideoxy-2,4-di-C-methyl-L -glycero- ((+)- 6 ) and -D -glycero-L -altro-heptono-1,4-lactone ((+)- 7 ), into (?)-(3R,4R,5R,6S)-3,4:5,7-bis(isopropylidenedioxy)-4,6-dimethylheptan-2-one ((?)- 22 ), and into (+)-(2R,3R,4R,5S,6S)-3,4:5,6-bis(isopropylidenedioxy)-2,4-dimethylheptanal ((+)- 34 ). Condensation of ((+)- 34 with the lithium enolate of (?)-(1R,4R,5S,6R)-6-exo-[(tert-butyl)dimethylsilyloxy]-1,5-endo-dimethyl-7-oxabicyclo[2.2.1] heptan-2-one ((?)- 38 ; derived from (+)- 1 ) gave a 3:2 mixture of aldols (+)- 39 and (+)- 40 (mismatched pairs of a α-methyl-substituted aldehyde and (E)-enolate) whereas the reaction of (±)- 34 with (±)- 38 gave a 10:1 mixture of aldols (±)- 41 and (±)- 39 . A single aldol, (?)- 44 , was obtained to condensing (+)- 34 with the lithium enolate of (+)-(1S,4S,5S,6S)-5-exo-(benzyloxy)-1,5-endo-dimethyl-7-oxabicyclo[2.2.1]heptan-2-one ((+)- 43 ; derived from (?)-(1S,2R,4S)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′S)-camphanate ((?)- 3 )). All these cross-aldolisations are highly exo-face selective for the bicyclic ketones. The best stereochemical matching is obtained when the lithium enolates and α-methyl-substituted aldehydes can realize a ‘chelated transition state’ that obeys the Cram and Felkin-Anh models (steric effects). Polypropionate fragments containing eleven contiguous stereogenic centres and tertiary-alcohol moieties are thus prepared with high stereoselectivity in a convergent fashion. The chiral auxiliaries ((1R)- and (1S)-camphanic acid) are recovered at the beginning of the syntheses.     

Enantiomerically pure 7-oxabicylo[2.2.1]hept-5-en-zyl derivatives as synthetic intermediates. Part III. Total synthesis of D- and L-ribose derivatives

Enantiomerically pure methyl 5-bromo-5-deoxy-2,3-O- isopropylidene-β-D - (D - 5b ) and -β-l-ribofuranoside (l- 5b ) have been derived from (?)-(1R,2S,4R)-2-exo-cyano-7-oxabicylo[2.2.1]hept-5-en-endo,-yl (1′S)-camphanate ( 1 ) and (+)-(1S,2R,4S)-2-exo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl(1′R)-camphanate ( 2 ), respectively, in 5 synthetic steps and 28% overall yield. Hydrolysis of D-5b and L - 5b afforded methyl 2,3-O isopropylidene-β-D -ribofuranoside (D -5a) and methyl 2,3-O-isopropylidene β-L-ribofuranoside (L-5a), respectively. The intermediate (+)-(1R,4R,5R,6R) 5-exo,6-exo-(isopropylidenedioxy)- 7 -oxabicyclo[2.2.1]heptan-2-one ((+)- 7 ) and its enantiomer(–)-7 were also obtained enantiomerically pure by resolution of (=)- 7 by the Johnson-Zeller method. In bothe approaches, the chiral auxiliaries ((–)- and (+)-camphanic acids, or (+)-(S)-N,S-dimethyl-S-phenylsulfoximide) were recovered at an early stage of the synthesis.     

Synthesis of (+)-1,3:2,5-dianhydroviburnitol ((+)-(1R,2R,3S,5R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol)

Epoxidation of (?)-(1R,2R,4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl acetate ((?)-5) followed by saponification afforded (+)-(1R,4R,5R,6R)-5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7). Reduction of (+)-7 with diisobutylaluminium hydride (DIBAH) gave (+)-1,3:2,5-dianhydroviburnitol ( = (+)-(1R,2R,3S,4R,6S)-4,7-dioxatricyclo[3.2.1.0^3,6]octan-2-ol; (+)-3). Hydride reductions of (±)-7 were less exo-face selective than reductions of bicyclo[2.2.1]heptan-2-one and its derivatives with NaBH₄, AlH₃, and LiAlH₄ probably because of smaller steric hindrance to endo-face hydride attack when C(5) and C(6) of the bicyclo-[2.2.1]heptan-2-one are part of an exo oxirane ring.     

The use of (−)-8-phenylisoneomenthol and (−)-8-phenylmenthol in the enantioselective synthesis of 3-functionalized 2-azabicyclo[2.2.1]heptane derivatives via aza-Diels-Alder reaction

The asymmetric aza-Diels-Alder reaction of the (1R)-8-phenylmenthyl or (1R)-8-phenylisoneomenthyl glyoxylate-derived N-benzylimine with cyclopentadiene resulted in the enantioselective synthesis of the corresponding pure [(1S,3-exo)-2-benzyl-2-azabicyclo[2.2.1]hept-5-ene]-3-carboxylates (80 or 69% yield, respectively). Reduction of these cycloadducts with LiAlH₄ afforded pure (−)-[(1S,3-exo)-2-benzyl-2-azabicyclo[2.2.1]hept-5-en-3-yl]methanol. Furthermore, a reaction sequence based on Barbier-Wieland degradation of both (1S,3-exo)-adducts afforded pure (+)-(1R)-2-benzoyl-2-azabicyclo[2.2.1]heptan-3-one. In the course of the two transformation sequences referred, the chiral auxiliaries were recovered in a virtually quantitative way.     

Some Transformations of (-)-(1S,4R)-1-Vinyl-7,7-dimethyl-bicyclo[2.2.1]heptan-2-one

Reactions were studied of (-)-(1S,4R)-1-vinyl-7,7-dimethylbicyclo[2.2.1]heptan-2-one with ethyl acetate lithium derivative, potassium acetylide, ozone, with a system OsO₄-N-methylmorpholine N-oxide, and some subsequent transformations of the products obtained.     

Cyclodimerization of 1-(Dimethoxyniethyl)-5,6-dimethylidene-7-oxa-bicyclo[2.2.1]hept-2-ene Induced by Nonacarbonyldiiron. Crystal Structure of (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)- Tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl)-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)]iron

The transition-metal-carbonyl-induced cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene is strongly affected by substitution at C(1) While 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept–2-ene-l-methanol ( 7 ) refused to undergo [4 + 2]-cyclodimerization in the presence of [Fe₂(CO)⁹] in MeOH, 1-(dimethoxymethyl)-5,6-di-methylidene-7-oxabicyclo[2.2.1]hept-2-ene ( 8 ) led to the formation of a 1.7:1 mixture of ‘trans’ ( 19, 21, 22 ) vs. ‘cis’ ( 20, 23, 24 ) products of cyclodimerization together with tricarbonyl[C, 5,6, C-η-(l-(dimethoxymethyl)-5,6-di-methylidenecyclohexa-1,3-diene)]iron ( 25 ) and tricarbonyl[C,3,4, C-η-(methyl 5-(dimethoxymethyl)-3,4-di-methylidenecyclohexa-1,5-diene-l-carboxylate)]iron ( 26 ). The structures of products 19 and of its exo ( 21 ) and endo ( 22 ) [Fe(CO)₃(1,3-diene)]complexes) and 20 (and of its exo ( 23 ) and endo (24) (Fe(CO)₃(1,3-diene)complexes) were confirmed by X-ray diffraction studies of crystalline (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)-tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl])-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)iron ( 21 ). In the latter, the Fe(CO)₃(1,3-diene) moiety deviates significantly from the usual local C_s symmetry. Complex 21 corresponds to a ‘frozen equilibrium’ of rotamers with η-alkyl, η³-allyl bonding mode due to the acetal unit at the bridgehead centre C(1).     

trans-Dichlorobis{(1R,4S)-1,7,7-trimethyl-3-[(S)-α-methylbenzylimino]bicyclo[2.2.1]heptan-2-one-N}Palladium(II): Synthesis and structural examination

A reaction of (1R,4S)-1,7,7-trimethyl-3-[(S)-α-methylbenzylimino]bicyclo[2.2.1]heptan-2-one with lithium tetrachloropalladate gave a chiral palladium(II) complex with monodentate coordination of the organic ligand. The structure of the complex was confirmed by NMR spectra and X-ray diffraction data.     

Microwave spectra and dipole moments of bicyclo [2.2.1]-hepta-7-one and bicyclo [2.2.1]hept-2-en-7-one

The microwave spectra of bicycle [2.2.1] hepta-7-one (I), bicyelo [2.2.1] hept-2-en-7-one (II), and exo-5,6-bisdeuteriobicyclo [2.2.1] hept-2-en-7-one (III) have been recorded in the region between 26.5 and 40.0 GHz. The rotational constants in the order A, B, C for the title compounds are 2773.24±0.31, 2301.74±0.04, and 2133.96±0.02 (I); 2979.22±0.08, 2418.60±0.01, and 2235.51±0.01 (II); and 2789.67±0.06, 2385.24±0.01, and 2150.60±0.01 (III). The rotational constants of four vibrationally excited states were also determined for (II). Quadratic Stark effect measurements on the 7₁₆ ← 6₁₅ transition of (I) gave ¦μ_a¦=2.99±0.03. Similar measurements on two 5 ← 4 and 4 ← 3 transitions of (II) gave ¦μ_a¦=2.88±0.03, ¦μ_b¦=0.39±0.03, ¦μ_c¦=0, and ¦μ_total¦=2.91±0.04.     

2-Chlorobicyclo[2.2.1]hept-5-ene-2-carboxamide and 2-chlorobicyclo[2.2.1]heptane-2-carboxamide as precursors of bicyclo[2.2.1]hept-5-en-2-one and bicyclo[2.2.1]heptan-2-one: resolution,absolute configuration and hydrogen-bonding properties

The absolute configuration of bicyclo[2.2.1]heptan-2-one has not been correlated with a crystal structure of a chemical precursor. The only chemical correlation available had an ambiguity, which could have reversed the assignment. Herein, we report the resolution of 2-chlorobicyclo[2.2.1]hept-5-en-2-exo-carboxamide on a cellulose triacetate column and the crystal structures of the enantiomerically pure and racemic α-chloroamide. We found the absolute configuration (1R,2R,4R) for the (+)-enantiomer of the α-chloroamide. This compound was converted to (+)-bicyclo[2.2.1]hept-5-ene-2-one by base hydrolysis, and the 5,6-unsaturated compounds converted to the saturated congeners. This is the first unambiguous experimental determination of the absolute configuration of bicyclo[2.2.1]heptan-2-one and of bicyclo[2.2.1]hept-5-ene-2-one. The three crystal structures of 2-chlorobicyclo[2.2.1]hept-5-en-2-exo-carboxamide reported herein reveal H-bonded dimers, with two distinct orientations of the bicyclic portion relative to the carboxamide dimer. In the racemic crystal, each dimer is composed of two enantiomers, and the bicyclic portions have their bridge carbon atom (C-7) on opposite sides of the H-bonded carboxamide dimer moiety. In the enantiomerically pure crystals, the major dimer had both C-7 atoms on the same side of the carboxamide dimer moiety while the minor dimer had the C-7 atoms on opposite sides. The dimers are present in solution, and can be easily monitored.     

Absolute Configuration of 3-Substituted 1-Azabicyclo[2.2.1]heptanes

The l-azabicyclo[2.2.1]heptan-3-exo-ol ( 2 ) was resolved by fractional crystallisation of its hydrogen tartrate salts. The enantiomers (+)- and (?)- 2 were oxidised to the ketones (?)- 4 and (+)- 4 , respectively (Scheme). CD spectroscopy suggested that (?)- 4 possesses the (1R,4S)-configuration. This absolute configuration was confirmed by single-crystal X-ray diffraction of the derivative (+)-(1R,4R)-3-(1,3-dithian-2-ylidene)-1-azabicyclo [2.2.1]-heptane ((+)- 5 ).     

Circular Dichroism of Tricarbonyl(diene)iron Complexes. The Octant Rule Applied to Ketones Perturbed by Remote Fe(CO)3 Groups. Crystal Structure of (±)-Tricarbonyl[(1RS,4RS,5RS,6SR)-C5,6,C-η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron

The preparation and the CD spectra of optically pure (+)-trans-μ-[(1R,4S,5S,6R,7R,8S)-C,5,6,C -η : C,7,8,C-η-(5,6,7,8-tetramethylidene-2-bicyclo [2.2.2]octanone)]bis(tricarbonyliron) ((+)- 7 ) and (+)-tricarbonyl[(1S,4S,5S,6R)-C-5,6,C-η-(5,6,7,8,-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron ((+)- 8 ), and of its 3-deuterated derivatives (+)-trans-μ-[(1R,3R,4S,5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C-η-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]-(octanone)]bis(tricarbonyliron) ((+)- 11 ) and (+)-tricarbonyl[(1S,3R,4S,5S,6R)-C-5,6,C- η-(5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone)]iron ((+)- 12 ) are reported. The chirality in (+)- 7 and (+)- 8 is due to the Fe(CO)₃ moieties uniquely. The signs of the Cotton effects observed for (+)- 7 and (+)- 8 obey the octant rule (ketone n→π*_CO transition). Optically pure (?)-3R-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone ((?)- 10 ) was prepared. Its CD spectrum showed an ‘anti-octant’ behaviour for the ketone n→π*_CO transition of the deuterium substituent. The CD spectra of the alcoholic derivatives (?)-trans-μ-[(1R,2R,4S, 5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]bis(tricarbonyliron) ((?)- 2 ) and (?)-tricarbonyl- [(1S,2R,4S,5S,6R)- C,5,6,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]iron ((?)- 3 ) and of the 3-denterated derivatives (?)- 5 and (?)- 6 are also reported. The CD spectra of the complexes (?)- 2 , (?)- 3 , (+)- 7 , and (+)- 8 were solvent and temperature dependent. The ‘endo’-configuration of the Fe(CO)₃ moiety in (±)- 8 was established by single-crystal X-ray diffraction.     

Syntheses and tandem Diels-Alder reactivities of 7,7-diphenyl-[2.2.1]hericene (= 7-(diphenylmethylidene)-2,3,5,6- tetramethylidenebicyclo[2.2.1]heptane) and 7-oxa[2.2.1]hericene ( = 2,3,5,6-tetramethylidenebicyclo[2.2.1]heptan-7-one)

Syntheses of 7,7-diphenyl[2.2.1]hericene ( 4 ) and 7-oxa[2.2.1]hericene ( 5 ) are presented. Rate constants k₁ and k₂ of the two successive Diels-Alder additions of ethylenetetracarbonitrile (TCE) to 4 and to 5 have been evaluated. At 25° in toluene, the rate-constant ratio k₁/k₂ = 260 and 21 for 4 and 5 , respectively. These results are compared with those reported for the tandem Diels-Alder reactivity of 2,3,5,6-tetramethylidenebicyclo[2.2.1]heptane and other derivatives.     

Optical resolution of 7-oxabicyclo[2.2.1]hept-21-ene derivatives. Diastereoselectivity in the formation of cyanohydrine-brucine complexes

A new, practical method for the optical resolution of bicyclic ketones if illusttrated by the preparation of (+)-(1R,4R)-7-oxabicyclo[2.2.1]bept-5-en-2-one ((+)- 1 ) and (+)-(1R, 2S,4R)-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yul acetate ((+)- 4 ). It involves the diastereoselective formation of a brucine complex with the corresponding cyanhydrine mixture.     

Stereoselective Double Friedel-Crafts Acylation of trans-μ-(2,3,6,7-Tetramethylidenebicyclo[3.2.1]octane)bis(tricarbonyliron). Crystal Structure of trans-μ-{(1RS,2RS,3SR,5RS,6SR,7SR)-C,2,3,C-η:C,6,7,C-η-[(Z,Z)-1,1′-(3,7-Dimethylidenebicyclo[3.2.1]octane-2,6-diylidene)di(2-propanone)]}bis(tricarbonyliron)

The Friedel-Crafts mono and double acylations of trans-μ-[(1RS,2RS,3SR,5RS,6SR,7SR)-C,2,3,C-η:C,6,7,C-η-(2,3,6,7-tetramethylidenebicyclo[3.2.1]octane)]bis(tricarbonyliron) ( 4 ) are highly stereoselective and yield trans-μ-{(1RS,2RS,3SR,5RS,6SR,7RS)-C,2,3,C-η :C,6,7,C-η-[(Z)-1-(3,6,7-trimethylidenebicyclo[3.2.1]-oct-2-ylidene)-2-propanone]}bis(tricarbonyliron) ( 5 ) and trans-μ-{(1RS,2RS,3SR,5RS,6SR,7SR)-C,2,3,C-η :C,6,7,C-η-[(Z,Z)-1,1′-(3,7-dimethylidenebicyclo [3.2.1] octane-2,6-diylidene)di(2-propanone)]}bis(tricarbonyliron) ( 6 ) whose structure has been established by single-crystal X-ray diffraction.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

Reactions involving transition metals: XX. A comparison of the reactions of 1,2,3,4,7,7-hexafluorobicyclo[2.2.1]heptadiene,and 2,3-bis(trimethyltin)- and 2,3-dichloro-1,4,5,6,7,7-hexafluorobicyclo[2.2.1]hepta-2,5-dienes with low valent transition metal complexes

1,2,3,4,7,7-Hexafluorobicyclo[2.2.1]heptadiene (1) and 2,3-bis(trimethyltin)-1,4,5,6,7,7-hexafluorobicyclo[2.2.1]hepta-2,5-diene (2) react with [M(Ph₃P)₄] (M = Pt, Pd) to afford air-stable adducts. 2,3-Dichloro-1,4,5,6,7,7-hexafluorobicyclo[2.2.1]hepta-2,5-diene (3) gives only [PtCl₂(PPh₃)₂] with [Pt(Ph₃P)₄], but a low yield of an adduct was obtained with [Pd(PPh₃)₄]. The diene 1 also reacts with Fe(CO)₅ to form the complex [(C₇H₂F₆)Fe(CO)₄], and with [Rh(C₂H₄)₂(acac)] to give [(C₇H₂F₆)Rh(acac)] in which the diene acts as a bidentate ligand. Similar products could not be isolated from the reactions of 2 and 3. A stable adduct, believed to be [{C₇F₆(SnMe₃)₂}Rh(CO)₂(μ-Cl)₂Rh(CO)₂] has been isolated from the reaction between 2 and [Rh(CO)₂Cl]₂. This adduct reacts with PPh₃ to give the bridge-cleavage product [{C₇F₆(SnMe₃)₂}RhCl(CO)(PPh₃)₂]. Reaction of 1 with [Rh(CO)₂Cl]₂ gives an unstable adduct which could not be isolated, and 2 does not react at room temperature. The chloro derivative 3 reacts with [PdCl₂(PhCN)₂] to give the adduct [(C₇F₆Cl₂)PdCl(PhCN)], but 1 and 2 do not react under similar conditions. Stable substitution products [(C₇F₆R₂)M] (R = H, M = Fe(CO)₂(η-C₅H₅); R = SnMe₃, M = Fe(CO)₂(η-C₅H₅), Mn(CO)₅, Ir(CO)₂(PPh₃)₂, Rh(CO)₂(PPh₃)₂; R = Cl, M = Ir(CO)₂(PPh₃)₂, Rh(CO)₂(PPh₃)₂) have been isolated from the reactions of the dienes with carbonylmetal anions. Insertion of the CHCH bond occurs when 1 is heated with [MnMe(CO)₅] to give [{C₇F₆H₂C($\text{O)Me}M}$n(CO)₄], and this, on reaction with either PPh₃ or [Pt(PPh₃)₄], gives [(C₇F₆H₂COMe)Mn(CO)₄PPh₃].