Acid Catalyzed Rearrangements of Structurally Constrained Tricarbonyl(trans-pentadienyl)iron Cations

Abstract

. Can. J. Chem. 52, 2085Chem. 52, (1974. Both the tricarbonyl(l,4-dimethylene-ci.~,c.is,tra~ts,cis-hexa-,3-dienyl)iron (secondary) and the tricarbonyl(l,4-dimethylene-5-methyl-cisScis,tra~~s-hexa-1,3-dienyl)iron (tertiary) cations, which cannot convert to a 'lr-cis pentadienyl system via a simple bond rotation, can be prepared at low temperature in strong acid media from their related alcohol complexes. The secondary as well as the tertiary ions rearrange to give the thermodynamically more stable tricarbonyl-(I-alkylcyclohexa-l,3-dienyl)iron cation via an acid catalyzed pseudo first order process. The rate of rearrangement of the secondary ion is much faster than that of the tertiary ion indicating a si~bstantial amount of residual positive charge on the exocyclic (B) carbon in the complexed tratu-pentadienyl carbonii~m ions.C. R. JABLONSKI et T. S. SORENSEN. Can. J. Chem. 52,2085Chem. 52, (1974. Partant descomplexes des alcools correspondants et travaillant a basse temperatureet dans iIn milieu fortement acide, on a pu preparer chacun des cations d~i (dimtthylene-1,4 cis,cis,tratu,ci.s hexadiene-1,3 yl) fer (secondaire) tricarbonyle et du (dimethylene-1,4 methyl-5 cis,cis,trat~s hexadiene-1,3 yl) fer (tertiaire) tricarbonyle q i~i ne peuvent Ctre transformes en iln systeme '11-cis pentadienyle par le moyen d'une simple rotation. L'ion secondaire de mCnie qile le tertiaire se rearrangent pour donner le cation thermodynanliqt~enlent le plus stable (alkyl-l cyclohexadiene-1,) yi) fer tricarbonyle grice Ll n processus depseudo premier ordrecatalyse par les acides. Le rearrangement de I'ion secondaire est beaucoup plus rapide qLle celui de I'ion tertiaire indiqllant qi~'une quantite importante de charge positive residuelle existe sur le carbone (B) exocycliq~~e dans les carbocations complexts trat~s-pentadienyle.[Traduit par le journal]The fact that acyclic tricarbonyl(tm7s-pentaThe obvious structural relationships of the ions dieny1)iron cations (1) are ubiquitous in their 1 and 3 with the profusely studied, yet still conrearrangement to give the related pe17tal7apto-troversial (6) ferrocenyl ion (5) has initiated tricarbonyl(cis-pentadieny1)iron cations (2) has been amply demonstrated (1-3). considerable discussion regarding the electroiiic structure of the trans-pentadienyl ion I. Intimately involved with any discussion of the electronic structure of 1 and 3 is a consideration of the driving force for the rearrangements 1 -+ 2 and 3 + 4.We have previously shown (3) that related trans-cis tricarbonyl(pentadieny1)iron cation pairs (e.g. 1 and 2) rapidly equilibrate a n d that in special circumstances conversion to apental7apro-tricarbonyl(cis-pentadieny1)iron complex is no guarantee of thermodynamic stability. It was of immediate interest then to investigate the stabilization modes available t o tricarbonyl (transCan. J. Chem. Downloaded from www.nrcresearchpress.com by 18.236.120.13 on 05/11/18For personal use only.

1,3-Cyclohexadien-1-Als: Synthesis, Reactivity and Bioactivities

“…In line with this, the above reaction sequence of organocatalytic synthesis of the cyclohexadiene carboxaldehyde unit and subsequent oxidation reaction has been used as a fair strategy for the preparation of multi-substituted aromatic aldehydes [62]. Scheme 45 Tricarbonyl iron complex of 1,3-cyclohexadiene-1-carboxaldehyde 1 has been prepared in a photochemical reaction with iron pentacarbonyl (Scheme 42) [75]. Such complex 197 was synthesized in the route to structurally constrained tricarbonyl (trans-pentadienyl) iron cations 199 to study acid catalyzed rearrangements.…”

“…Tricarbonyl iron complex of 1,3-cyclohexadiene-1-carboxaldehyde 1 has been prepared in a photochemical reaction with iron pentacarbonyl ( Scheme 42 ) [ 75 ]. Such complex 197 was synthesized in the route to structurally constrained tricarbonyl ( trans -pentadienyl) iron cations 199 to study acid catalyzed rearrangements.…”

“…Such complex 197 was synthesized in the route to structurally constrained tricarbonyl (trans-pentadienyl) iron cations 199 to study acid catalyzed rearrangements. Tricarbonyl iron complex of 1,3-cyclohexadiene-1-carboxaldehyde 1 has been prepared in a photochemical reaction with iron pentacarbonyl (Scheme 42) [75]. Such complex 197 was synthesized in the route to structurally constrained tricarbonyl (trans-pentadienyl) iron cations 199 to study acid catalyzed rearrangements.…”

Transition-metal mediated asymmetric synthesis. Part 3. Preparation and stereospecific alkylation of unsymmetrically substituted tricarbonyl(cyclohexadienyl)iron(1+) salts: an organometallic approach to the synthesis of carvone, cryptomerion, and bilobanone

“…tvzcarbunyZ( 1-4-q-5P-methyZcyclohexa-l13-diene)iron(0) (2b) (0 31 g, 1%) was obtained b y distillation a t 35 "C (at 10F mmHg) as a golden oil [(Found: C,51.65;H,4.6. C,,Hl,FeO,requires C,51.32; H, 4.31%); vmax, (cyclohexane) 2 040 and 1 971 cm-l; v , , (liquid film) 1 375, 1332, and 965 cm l ; G(CDC1,) 0.88 (3 H , d , J 7 Hz, Me), 1.35-2.05 (3 H, m, 5a-, 6a-, 6p-H), 2.94 (1 H , d t , 4-H), 3.15 (1 H , ni, 1-H), and 5.05-5.35 (2 H , m, 2-, 3 -H ) ; m/z 234 ( M + , 2%), 206 (25), 178 (14), 162 (lo), 148 ( 16), and 134 (loo)] ; tvicarbonyZ( 1-4-r)-2-methoxy-3-metJzyZ~ycZohexa-1,3diene)iron(o) (2c) was obtained as a yellow solid (2.46 g, 10%); vlllrLY, (cyclohexane) 2 033, 1 964, and 1 955 an-'; v,,,~ (loo), 176 (7), 162 (8), and 148 (15). A sample was crystallised from pentane a t -78 "C for analysis, m.p.…”

“…(3 H , m, 6a-, 5-H), 2.11 (3 HI s, Me), 2.28 (1 H, m, 6p-H), 2.75 (1 HI m , 4-H), 3.49 (3 H, s, OMe), and 4.98 (1 H , d, J 6 Hz, 3-H); m/z 264 (M', 2%), 236 (20), 208 (6), 206 (14), 178 (loo), 176 (6), 162 (9), and 148 (14). TrzcurbonyZ(1-4-ql-methoxy-6-methyZcycZohexa-1,3-diene)iron(0) was obtained as a 1 : 2 mixture of epimers (2f) and (2g) after distillation a t 30-45 "C (at mmHg) in the form of a golden'oil (0.63 g, 206 (18), 178 (loo), 176 (!I), 164 (30), 148 (19), and 134 (S)], and subsequent chemical reactions (see below) are consistent with the above formulation.…”