Synthesis and characterization of some transition metal complexes of alkylisocyanobenzoates

Ne ELSEVI ER

InorganicaChimicaActa 264 ( 1997) 161-169

Synthesis and characterization of some transition metal complexes of alkylisocyanobenzoates Marjorie E. Squires ", Andreas Mayr ~ . b . . , I ~'Department of Chemistry. State Universi~" of New York at Stony ~rook. Stony Brook. NY I 1794-3400. USA b Department of Chemistry. Tile Universi O"of Hong Kong. Po£~dam Road. Hong Kong. Hong Kong

Received 10 February 1997; revised l0 March 1997: accepted5 May 1997

Abstract

The alkyli,';ocyanobenzoates 1 (a: CNC,H.L-CO_,Me-4; b: CNC,H4-CO_,Et-4; c: CNC,H4-CO-z_Me-3) were prepared. Reaction of [ Fc( T/sCsH~)CI(COhl with la,b in refluxing benzene, followed by ion exchange with NH,~PF, in acetone affords the complexes [Fe(1fCsH~)(CNC6H4-CO:R-4)d[PF,] (2a,b). The complexes [Felz(CNC,H4-CO_,R)41 (3a-.c). [CoI_,(CNC6H~-COzMe-4).d ( 4 ) a n d [ PdI2(CNC,H4-COzMe-4)2 ] (5) form in the reactions of the metal iodides with the respective isocyanides. The .solid state structures of 3b, 4 and 5 were determined by X-ray crystallography. 3b: space group P'2~/c, a = 9.042( I ), b = 17.424( I ), c = 13.417( I ) .~./3= 90.92( ! )°, Z = 2 . 2427 unique reflections, R=0.029, R~ =0,038. 4: space group P-I, a = 12.060(6), b = 13.316(8), c = 15.67( I ) A, a=79.23(4), /3=81.16(4), 7=62.66(6) °, Z=2, 3206 unique reflections, R=0.053, Rw=0.063. 5: space ~oup P-l, a=7.796(2), b=8.012(2), c=~.~62(2)A~ct=7~.42(2)~=68.~5(2)~=66~9(2)°~Z=~6~8~niqueref~ecti~ns~R=~22~R~=~.~29. 1997Elsevier Science S.A. Keywords: Crystal structures: Iron complexes:Palladiumcomplexes:Isocyanidecomplexes

1. I n t r o d u c t i o n

lsocyanide transition metal complexes [ ! ] possess steric and electronic properties which make them attractive as building blocks for molecular materials [2l. Their coordination geometries are well-defined, and there is good electronic contact between the metal centers and (unsaturated) organic groups due to the presence o f partial metal-carbon multiple bonds. The controlled self-assembly [31 of such building blocks into molecular solids, mediated by peripheral weak interaction sites, promises to be a useful method for the synthesis o f novel materials. We have recently developed metal isocyanide complexes containing nitrogen donor groups as a suitable class of molecular building block [4,5l and have demonstrated the formation of coordination polymers in combination with unsaturated metal complexes or metal ions [ 4 I. The range of materials accessible by the selfassembly of isocyanide metal complex building blocks would be broadened significantly, if the versatility of hydrogen bonding groups 161 could be made use of. This potential, however, is not easily realized, since typical hydrogen bond* Correspondingauthor. Tel.: + 825-2859 7919: t:ax: + 825-2557 1586. J On leave at The Universityof Hong gong. 0020-1693/97/$17.00 © 1997 El~vier ScienceS.A. All rights reserved PII SUU2O- 1693 ( 97 ) 05604- I

ing groups are not compatible with the usual preparative routes to isocyanides [ 7 ] ". The synthesis o f the desired systems would require the development o f new synthetic strategies in which the introduction o f the hydrogen bonding sites is postponed until after the formation o f the isocyanide functionality and possibly even after coordination o f the isocyanides to transition metal centers [ 9] 3. As a possible approach, we considered functional group transformations o f the ester groups of alkylisocyanobenzoates. Ester groups are potential precursors for hydrogen bonding sites, such as carboxylic acid or amide groups. These considerations prompted us t.o synthesize transition metal complexes o f isocyanobenzoic acid esters [ I i ]. The solid-state structures o f three examples were determined by X-ray crystallography. -"A small numberof isocyanideswith functionalgroupscapableof hydrogen bondinga~ known [8 I. e.g. CNCHRCHR'OH ( R = Et, R' = H: R = H, R' =Me). CN(CH~).OH (n =2, 3, 5) (a), CNC,t'LCO:H-4 (b), CNCHArCONHR (e.g. Ar=4-CIC,H4. I-naphlhyl:.R=c-C,H~, C,H~CH2) (eL CNCH_,CH2NHCOR ( R = CH~.C,H~) (d). CNCHRCONHR° (e.g. R = IlL CH,: R' = c-C,H~~,C.,H~CH,) ~e ). A numberof coordinatedisocyanidescarryinggronp~capableof hydrogen bondinghave been generatedby 'additionof hych'ogonisocyanidemetal complexes to epoxides and beteroallenes,by reduction of y-oxoalkylisocyanide ligands, arid by hydrolysisof siloxypbenylisocyanitleand isocyanoacetic acid ester ligands.See. for examples.Ret: 110I.

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2. Experimental Standard inert-atmosphere techniques were used in the execution of the experiments. The solvents methylene chloride, hexane (CaHz), benzene, ether, tetrahydrofuran (Na/ benzophenone) and acetonitrile (P_,Os) were dried and distilled prior to use. [Fe( r/5-CsHs)CliCO),] wa~ prepared as previously reported [12]. All other reagents were used as obtained from commercial sources. The NMR spectra were measured at 250 or 300 MHz (for ~H NMR) at room temperature, unless otherwise noted: solvent peaks were used as internal reference; the chemical shifts are reported in 6 relative to TMS. Elemental analyses were performed by M-H-W Laboratories. 2. I. S3wtheses 2.1.1. Methyl-4-isot:vanobenzoate (la) Acetic formic anhydride is first prepared by heating a mixture of lbrmic acid ( 27.9 ml, 0.739 mol ) and acetic anhydride ( 67.0 ml, 0.710 mol ) to 50°C for 2 h. The mixture is allowed to cool to room temperature. A mixture of 4-amino-methylbenzoate (5.022 g, 33.22 mmol) and acetic formic anhydride (25 ml) is stirred for 71 h at room temperature [ 13]. Then all volatile components are removed under vacuum. The formed 4-formamido-methylbenzoate is washed several times with hexane and dried under vacuum. A solution of 4-formamido-methylbenzoate (2.019 g, !1.27 mmol) and triethylamine (3.93 ml, 28.2 mmol) in methylene chloride (30 ml) is cooled to 0°C, and a solution of phosgene in toluene (11.8 mmol) is added slowly by syringe with stirring [7 ]. A colorless precipitate forms. The mixture is stirred for 2 h, during which time the solution is allowed to warm to room temperature. Then, a few ml of water are added. After a few additional minutes, the methylene chloride solution is washed several times with water. The methylene chloride layer is dried over sodium sulfate and sodium carbonate. The solution is filtered, and the solvent removed under vacuum. The residue is extracted several times with hexane. The combined extracts are filtered, and the solvent is removed under vacuum. The resulting residue is sublimed to afford a white solid (0.784 g, 43%). The product is stored at -40°C. *H NMR (CDCI3): 6 8.09 (d, 2H, Ph), 7.46 (d, 2H, Ph), 3.93 is, 3H, CH3). IR (KBr, cm-~): 2125 (s), 1735 (s), 1720 is), 1605 (m). 2.1.2. Ethyl-4-isot3'anobenzoate ( lb ) This compound was prepared following the procedure described for la, using 4-formamido-ethylbenzoate ( 1.510 g, 7.81 mmol), NEh (2.72 ml, 19.5 mmol) and phosgene (8.11 mmol), and 25 ml methylene chloride. Pale yellow solid (0.73 g, 51%). The product is stored at -40°C. *H NMR (CDCh): 6 8.09 (d, 2H, Ph), 7.44 (d, 2H, Ph), 4.39 (q, 2H, CH,), 1.39 (t, 3H, CH~). ~3C NMR (CDCIO: 6 167.0, 164.9, 131.3, 130.8, 126.4, 61.6, 14.2. IR (KBr, era-L): 2130 (s), 1718 (s), 1606 is).

2.1.3. Methyl-3-iso~;vanobenzoate ( lc) This compound was prepared following the procedure described for la, using methyl-3-formamido-benzoate (2.543 g, 14.19 mmol), NEt3 (4.95 ml, 35.5 mmol) and phosgene ( 14.9 mmol), and 40 ml methylene chloride. White crystalline solid ( 1.290 g, 56%). The product is stored at -40°C. ~H NMR (CDCI3): 68.09 (s, IH, Ph), 8.06 (d, 2H, Ph ), 7.56 ( m, 2H, CH ), 3.95 ( s, 3H, CH3). IR ( KBr, cm - J): 2127 (s), 1716 (s). 2.1.4. [Fe(TIs-CsHs)(CNC~H4COeMe-4)3]PF~(2a) A solution of [FeiT/5-CsHs)CIiCO)2] (0.663 g, 3.121 retool) and 4-isocyanomethylbenzoate (I.525 g, 9.463 mmol ) in 40 ml benzene is heated to reflux for 1.75 h. After cooling to room temperature, the solvent is removed in vacuo, and the residue is washed with hexane. The solid is redissolred in acetone, and NH4PF6 ( 1.046 g, 6.417 mmol) is added. The mixture is stirred for 2.5 h and then filtered through a fritted disk covered with cellulose. The flask and filter aid are rinsed with a small amount of additional acetone. The solvent is removed from the clear brown filtrate by applying vacuum, and the residue is redissolved in CH2CI2. The resulting solution is again filtered through a flitted disk covered with cellulose. The filtrate is taken to dryness in vacuo. The solid is then extracted with hot ethanol, and the resulting solution filtered through a plug of glass wool. Upon cooling, 1.387 g of light brown crystalline needles form (59%). M.p. 174175°C. ~H NMR (CDCI3): 68.06 (6H, CH), 7.57 (6H, CH). 5.24 (5H, C5H5), 3.90 (9H, CH3). IR (KBr, cm-~): v ( C N ) = 2 1 7 2 (m), 2120 (s); v ( C = O ) = 1 7 2 3 is); v ( C = C ) = 1601 (s). Anal. Calc. for C32H26N306FePF~,: C, 51.29; H, 3.50; N, 5.6 I. Found: C, 5 I. I I ; H, 3.70; N, 5.46%. 2.1.5. [ Fe( *ls-C~H.~)(CNC~H4CO,Et-4 )3]P F6 (2b ) The procedure described above for la was followed, using 0.406 g [Fe(r/5-CsHs)Cl(CO)_,l ( 1.9!1 mmol) and 1.018 g ethyl-4-isocyanobenzoate ( 5.811 mmol) in 25 ml benzene, and 0.627 g NH4PF~, (3.85 tnmoi): Golden crystals (0.682 g, 80%). M.p. 209°C. ~H NMR (CDCI3): 6 8.08 (d, 6H, C~,H4), 7.58 (d, 6H, C6H4), 5.25 ( s, 5H, C5H5), 4.36 (q, 6H, CH_,), 1.36 it, 9H, CH3). IR ( KBr, c m - ~): u(CN) =2176 (m), 2125 (s), 2102 (s); l,(C=O) = 1722 is), 1712 is); ~,(C=C) = 1601 (s). Anal. Calc. for C3sH3.,N~O6FePF6: C, 53. I I; H, 4.075; N, 5.3 I. Found: C, 51.68; H, 4.32; N, 4.97%. 2.1.6. Trans-[Fel,_(CNC~H4CO2Me-4)4] (3a) Felz.4H20 (0.127 g, 0.410 retool) is placed in a 50 ml Schlenk flask and and dried for I h with gentle heating. Then methyl-4-isocyanobenzoate (0.270 g, 1.68 mmol) and 20 ml THF are added. The reaction solution is stirred for 6 h at room temperature and then taken to dryness in vacuo. The residue is washed with hexane and redissolved in THF. Upon slow addition of diethyl ether, a green crystalline solid precipitates (0.195 g, 50%). IH NMR (CDCI3): fi 8. I I (d, 8H, C6H4), 7.63 ( d, 8H, C6H4), 3.94 ( s, 12H, CH3). IR ( KBr, cm - J): ~,(CN)=2120 (s), 2109 is), 2046 (sh), 1995 (sh);

M.E. Squires. A. Mayr/ Inorganica ChimicaAcre264 ( 1997~161-169

163

z,(C=O) = 1713 (s); ~,(C=C) = 1599 is). Anal. Calc. for C36HasOsN4FeI2: C, 45.31; H, 2.96; N, 5.87; Fe, 5.85. Found: C, 47.31 ; H, 4.85; N, 4.50; Fe, 6.49%.

= 1599 (m). Anal. Calc. for C,aHz404NzPdI2: C, 31.68; H, 2.07; N, 4.10; Pd, 15.59. Found: C, 31.78; H, 2.12; N, 4.04; Pd, 15.81%.

2.1.7. Trans-lFel,_(CNCdt4CO2Et-4)jl (3b) FeI2.4H_~O (0.240 g, 0.629 mmol) is placed in a 50 ml Schlenk flask and heated to about 50°C for I h. Then ethyl4-isocyanobenzoate (0.556 g, 3.17 mmol) and 25 ml THF are added. The reaction solution is stirred for 6 h at room temperature and then taken to dryness in vacuo. The residue is washed with hexane and redissolved in THF. Upon slow addition of diethyl ether, a green crystalline solid precipitates (0.504 g, 64%). M.p. 175°C. ~H NMR iCDCI3): ~ 8.11 (d, 8H, C6H4), 7.63 (d, 8H, C6H4), 4.38 (q, 8H, CH2), 1.40 (t, 12H, CH3). IR (KBr, c m - ' ) : u(CN)=2121 (s); uiC=O) = 1713 (m); u ( C = C ) = 1600 im).Anal. Caic. for C4oH36N4OsFeI2: C, 47.55; H, 3.59; N, 6.34; Fe, 5.53. Found: C, 47.82; H, 3.80; N, 6.07; Fe, 5.73%.

2.1.11. Reaction of 2b with BBr.~and MeOH A solution of 2b (0.201 g, 0.308 retool) in 25 ml of CH2C12 is cooled to - 78°{2 and excess boron tribromide ( !.25 ml of ! M solution) is added. The mixture is first stirred for 16 h at room temperature and then under reflux for 1.5 h. After cooling to room temperature, the solvent is removed to give a yellow solid. IH NMR (CDCi3): 6 8.12 (d, 6H, C6H4), 7.77 (d, 6H, C6H4). 5.62 is, 5H, CsHs). IR (KBr, cm-~): v(CN) =2171 (m), 2117 (s); r ( C = O ) = 1769 (m). The solid obtained this way is dissolved in methanol. After 24 h, all volatile components are removed under vacuum. ~HNMR (CDCI3): 6 8.10 (d, 6H, C6H4), 7.92 (d, 6H, C6H4), 5.64 is, 5H, C5H5), 3.90 (s, 9H, CH3). IR (KBr, c m - I ) : 2171 (m), 2117 (s); u~C=O) = 1717 (m), 1598 (m).

2.1.8. Trans-[Fel,_(CNC6H4COzMe-3)4] (3c) This compound was synthesized following the procedure described for 3a. The reagents used were methyi-3-isocyanobenzoate ( 0.165 g, 1.02 mmol ) and Fel_, (0.075 g, 0.242 mmol). Green crystalline solid (0.090 g, 39%). tH NMR (CDCIO: 8 8.21 (s, IH, CH), 8.08 (d, IH, CH), 7.77 (d, IH, CH), 7.57 (t, IH, CH), 3.93 is, 3H, CH3). IR (KBr, c m - ~): 2123 (s), 1724 is).

2. !. 12. Reaction of 3a with HC! Conc. HCI (0.10 m i) was added to a stirred solution of 3e (0.022 g, 0.023 mmol) in 10 ml of CH2C!2. The reaction was monitored by IR, but little change was observed. The reaction mixture was stirred for 95 h, then H20 w ~ added. A few minutes later, the solution was stripped to dryness. The residue was dissolved in THF and dried over magnesium sulfate. The green solution was filtered and then taken to dryness under reduced pressure, The residue was washed with hexane. A clean product was not isolated, but the IR spectrum showed that a major portion of the solid was unreacted starting material. IR (KBr, cm-~): 2118 (m), 1725 (m).

2.1.9. Trans-ICol,.(CNCJ-14CO2Me-4)4] (4) A solution of methyl-4-isocyanobenzoate i0.418 g, 2.59 mmol) in 20 ml acetonitrile is added to a hot (80°C) green solution of Coi2 (0.113 g, 0.362 mmol) in 50 ml acetonitrile. The dark reaction mixture is stirred at 80°C for 2 h. After cooling to room temperature, the solvent is removed in vacuo. The residue is washed three times with 20 ml of hexane and then redissolved in acetonitrile. The resulting solution is filtered, and the solvent removed under vacuum to give a dark brown crystalline solid (0.210 g, 61%). M.p. 150°{2. 'H NMR (acetone-d°): & paramagnetic, broad signals 8.12, 8.0 I, 7.8 I, 3.85, 2.8 !, 2.03, O. 12. IR ( KBr, cm - ~): u(CN) =2170 (s, br); u(C=O) = 1718 (s); u(C=C) = 1599 (m). Anal. Calc. for C38H_,aO~N4Co12: C, 45.16; H, 2.95; N, 5.85; Co, 6.16. Found: C, 44.90; H, 2.74; N, 5.76; Co, 6.03%. 2.1.10. Trans-lPdl,_(CNCd-14CO,_Me-4),_] (5) A solution of methyl-4-isocyanobenzoate (0.444 g, 2.76 mmol) in a few ml of acetonitrile is added to a stirred hot (80°C) mixture of Pdl2 i0.448 g, 1.24 mmol) and 25 ml acetonitrile. An orange precipitate forms. After stirring for 2 h at 80°C, the reaction mixture is allowed to cool to r~om temperature. The solvent is removed in vacuo. The orange residue is washed three times with 20 ml of hexane, dried, and recrystallized from CHCI3/hexane (0.661 g, 78%). M.p. 245°C. ~H NMR (CDCI0: ~ 8.18 (d, 4H, C6H4), 7.63 (d, 4H, C6H4), 3.97 (s, 6H, CH3). IR (KBr, cm-~): u(CN) =2196 is). 2165 (sh); u ( C = O ) = i 7 1 7 is); u(C=C)

2.1.13. Reaction of 3a with piperidine Piperidine (0.10 ml) was added to a solution of 3a ( 0.049 g, 0.051 mmol ) in THF ( i0 ml). The reaction was monitored by IR. Only a little change was observed for several days. After 5 days, the solvent was removed under reduced pressure, and the residue was washed with bexane. The product was then treated with diethyl ether and THF. A clean product was not obtained, but a green solid extracted from the residue with diethyl ether exhibited IR absorptions which were in good agreement with those of the starting material. IR (KBr, cm-m): 2124 (m), 1718 (m). 2.2. Crystallographic studies The molecular structures of complexes 3b, 4 and 5 were determined by X-my crystallography. The general proceOares for unit cell determination, datacollection, and structuresolution have been previously described in detail [ 14]. All intensity measurements were made on an Enraf-No.~ius CAD4A automated diffractometer, using a variable-rate. ¢a-20 scan technique. Empirical absorption corrections (DIFABS [ 15 ] ) were applied. All calculations were performed using the TEXSAN programs [ 16]. The structures were solved by

164

M.E. Squire~'. A M a y r / Inorganica Chimica Acta 264 (1997) 161-169

Table I

CD'stallographicdata for complexes3b. 4 and 5 Formula a (A)

C4oH~.FeI2N40~ 9.042( 1 )

C4.H.~CoI2N4Ox 12.060(6)

C,aH,4PdI2N204 7.796(2)

b (A) c (A) a (°) /3 ( ° ) .,/( ~ )

17.424( I ) 13.417( 1 ) 90.000 90.92( I ) 90.000

13.316(8) 15.67( I ) 79.23 ( 4 ) 81.16(4) 62.66(6)

8.012(2) 10.162(2) 71.42( 2 ) 68.15(2) 66.19( 2 )

V(,~ ~)

21 i 3 . 6 ( 4 )

2189(2)

528.3(2)

Z Space group Temperature Radiation ( graphite monochromator).A ( A ) Linear absorptioncoefficient( cm ') Scan mode 20 Range (°) Unique reflectionswith If,,I " > 3~rIF,.I-" Final no. variables R" = F-I IF,,I- IF~I I/EIF,,I R~ = [ Ew( IF,,I - IF,[ )-"/En'F.,-"I Lj-" Standard error in observationof unit weight

2 P2,/c ambient Mo Koz.0.71073 18.524 0/20 0<20<50 2427 250 0.029 0.038 1.691

2 P- I ambient Mo Ka. 0.71073 18.385 0/20 0<20<50 3206 484 0.053 0.063 2.521

1 P- I ambient Mo Kot.0.71073 37.825 0/20 0<20<50 1618 124 0.022 0.029 1.434

Quantity minimized

( Y'w( I F . I - I k'~ I )" ): w e i g h t w = I / ( tr" + 0.0016F.,-" ).

direct methods and difference Fourier methods. Selected crystallographic data for 3b, 4 and 5 are listed in Table 1. 3. Results and discussion Methyl-4-isocyanobenzoate ( l a ) , ethyl-4-isocyanobenzoate ( l b ) and methyl-3-isocyanobenzoate ( I t ) were chosen as the isocyanide ligands for this study. The complexes 2a,b form upon reaction o f [ Fe(r/5-CsHs)CI(CO) 21 with the isocyanides l a , b in hot benzene and subsequent treatment with NH~PF6 in acetone (Eq. ( I ) ) [ 171. Light brown and golden crystals o f 2a attd 2b, respectively, are obtained by recrystallization from ethanol. Reaction of iron(ll) iodide with the isocyanides la.--c in THF and recrystallization from THF/ether affords the complexes 3a--c as deep green crystals (Eq. ( 2 ) ) [4,18]. Addition o f l a to a hot solution o f Col_, in acetonitrile gives complex 4, which is isolated in the form of dark brown crystals [ 19]. Pdl2 reacts in a similar fashion with l a to give 5. Complex 5 forms orange crystals from CHCI.dhexane 1201. C--N--~la:

CO2R

C--N-~

R = CH 3

lb: R =

CO2Me

1C

C2H 5

lie("0s-CsH~) CI( CO)2I I, I/Clt2C'I2

--, 2. NH4PFt, I;Lcchme

[Fe( r/s-CsH~)L~ ] PF~,

(I)

.~1:1. ~ l a Zb: I . . I b

!

MI2

~ Till:or CIIK'N

trans-lMl2L,,I 3a: M = to: I , = la. u 3b: M Fc; I. Ib: n

(2) -I 4

4: M , (',,: . u: ,, 4 .g: M I'd: I. : I11; ,~ 2

Complexes 2-5 give rise to characteristic IR absorptions for the isocyanide and carbonyl groups. The IR spectra o f the cationic iron(ll) complexes 2 feature two absorptions at about 2170 and 2120 c m - J , indicating local C3,. symmetry o f the iris (isocyanide) iron fragment. The neutral iron ( II ), cobalt(ll) and palladium(II) iodide complexes 3, 4 and 5 exhibit only single stretching frequencies at about 2120, 2170 and 2200 c m - ~, respectively. These data are in agreement with a t r a n s arrangement o f the iodide ligands in these systems. The stretching frequencies of the alkoxycarbonyl groups appear in the range between 1710 and 1725 cm-~. The ~H NMR spectra o f complexes 2, 3 and 5 are very simple, featuring only the resonances for the arene rings and the alkoxy groups and, in the case of complexes 2, a resonance for the cyclopentadienyl ligand. The paramagnetic cobalt( II ) complex 4 gives rise to several less distinct and broad JH NMR resonances. The solid state structures of the complexes 3b, 4 and 5 were determined by X-ray crystallography. The crystallographic data tbr all three compounds are listed in Table I. The atomic coordinates are given in Tables 2-4, and selected bond distances and bond angles are listed in Table 5. Phe molecular structures of complexes 3b, 4 and 5 are shown in Fig. I (a), Fig. 2 (a) and Fig. 3 (a), respectively. The intramolecular bonding parameters o f all three compounds are within the range established for structures o f the same types 14.18.19 I. The coordination geometries of the iron and cobalt complexes 3b and 4 can be described as octahedral, that o f the pahadium complex 5 as square planar. The structures conlirm the t r a n s configuration of the iodide ligands in all three compounds. The ligand sets of the iron and cobalt complexes 3b and 4 differ only in the nature of the ester substit,'c;;i~ t Jb: R = Et; 4: R = Me), yet the molecular as well as the crystal structures exhibit distinct differences. The cobalt-

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M.E. Squires. A. Mayr / Inorganica Chimica Acta 264 (19971 161-169

Table 2 Final atomic coordinatesand B{qvaluesof complex3b

Table 3 Final atomiccoordinates and B¢,~valuesof complex4

Atom

x

y

z

B~I

Atom

x

I(I) Fe(I) O( I ) 0(2) 0(3) 0(4) N( I ) N(2) C( I ) C(2) C(31 C(41 C(5) C(61 C(7) C(8) C(9) C(10) C(II) C( 121 C( 131 C(14) C( 151 C( 161 C( 171 C(18) C(191 C(201

8.80456(3) 1.0000 1.5096(41 1.6051(4) 0.9093(3) 1.1384(4) 1.2269(4) 1.0576(4) 1.1423(41 1.3060(4) 1.2883(4) 1.3629(4) 1.4550(41 1.4753(51 1.3999(51 1.5340(5) 1.5712(71 1.5030(81 1.0351(41 1.0545(4) 0.9479(5) 0.9420(4) 1.0460(4) 1.1541(4) 1.1595(4) 1.0392(51 0.8901(5) 0.7328(6)

0.61179(2) 1/2 0.9247(2) 0.9301(2) 06710(21 0.6325(2) 0.6235(2) 0.5237(21 0.5750(2) 0.6906(2) 0.7259(21 0.7922(21 0.8240(2) 0.7880(3) 0.7202(3s 0.8980(3) 1.0006(31 1.0273(41 0.5119(21 0.5533(2) 0.6065(2) 0.6359(21 0.6128(2) 0.5605(2) 0.5304(2) 0.6399(2) 0.6981(3) 0.7224(3)

0.01363(2) 0 -0.1967(31 -0.0422(3) 0.6308(2) 0.6698(2) - 0.0321 ( 21 0.2194(2) - 0.0217(21 -0.0511(3) -0.1420(3) -0.1607(31 -0.0894(3) 0.0001(3) 0.0193(3) -0.1050(4) -0.2188(61 -0.3093(6) 0.1362(3) 0.3170(21 0.3388(3) 0.4344( 31 0.5052(3) 0.4804(2) 0.3866(3) 0.6105(3) 0.7323(3) 0.7419(3)

5.34(2) 3.26(3) 6.5(2) 7.6(2) 4.5(I) 6.8(2) 4.7(2) 4.1(I) 3.8(2) 3.8(2) 4.4(2) 4.4(2) 3.9(2) 5.6(2) 5.6(21 5.2(2l 8.7(4) 10.7(5) 3.7(2) 3.5(2) 4.2(2) ~.0(2) 3.4( I ) 3.6(2) 3.7(2) 4.0(2) 5.2(21 5.9(2)

I( I I I(21 Co(I)

0 . 4 5 5 9 6 ( 7 ) 0.77879(7) 0 . 8 0 1 5 0 ( 7 ) 0.49603(7) 0.6161(I) 0.6345(I) -0.0220(9) 0.478{ I ) 0.0925(71 0.3115(81 0.3895(8) 1.2203(8) 0.2860(8) 1.1314(7) 0.831(I) 1.1451(81 0.9651(81 0.9949{7) I.1184(9) - 0.018( I ) 1.219( I ) 0.086( I ) 0.4242(9) 0.5540{ 8)

iodine bonds (av. 2.86 ,g,) are significantly longer than the iron-iodine bonds (2.64 A). This feature can be atuibuted to the influence of the singly occupied d:_- orbital of the cobalt( Ill center. The Fe--C and C o - C distances of the equatorial isocyanide ligands on the other hand are very similar in both complexes. Even though the complexes plepared in this work do not contain any specific directional intermolecular interaction sites, it is of interest to consider the crystal structures of the complexes 3b, 4 and 5. In each case, the packing of the molecular units appears to be influenced by weak or-or interactions between the isocyanobenzoate groups. The "square" tetrakis(isocyanide)metal units of 3 b are joined via these or-or contacts to form layers, those of 4 are arranged in rows. A view of a layer of the crystal structure of 3b is shown in Fig. I ( b ) . Each joint between the molecular units of 3b consists of a stack of four isocyanobenzoate groups. The shortest intermolecular carbon-carbon distances between the inner pair of ethylbenzoate groups are in the range 3.45-3.54 A, indicating ¢r contacts of average strength [ 21 ], while the shortest contacts involving the outer groups are 3.52-3.72 A,. The two views of a row of laterally joined molecular units of 4 in Fig. 2 ( b ) illustrate the overlap of the arene groups and the 'above-below-above-below" alternation of the 'square' molecular units. The closest carboncarbon distances between the arene groups are in the range 3.56-3.75 A, suggesting the presence of only moderate ¢r-~" interactions [20]. The isocyanide ligands in the solid state

o( I )

0(2) O(3) O(41 0(5) 0(6) O(71 0(8) N( I )

y

z0.96444(6) 1.21889(6) 1.1005(I) 1.4117(71 1.3623(61 1.4312(6) 1.5146(6) 0.7402(7) 0.6744(6) 0.8433(8)

0.7817(81 1.1833(71

B~ 5.88(8) 6.17(8) 4.7(I) 9( l ) 6.8(9) 7(I) 6.6(9) 9(I) 6.6(9) 9( I )

13( I ) 5( I )

N(2)

0.5047(9)

0.819(I)

1.2167(71

5(I)

N(3)

0.7703(8)

0.7452(8)

0.9966(6)

5(I)

N(41 N(5 ) N(6) C( I ) C(21

0.767( I 1 0.761 ( I ) 0.519( I ) 0.499( I ) 0.333( I )

0.442( 1 ) 0.198( I ) 0.396( I ) 0.581 ( I ) 0.521 ( I )

0.9952(7) 0.444( 1 ) 0.607( I ) 1.1509( 81 1.2266(81

6( I ) 10.6(4) I 1.2(4) 5( I ) 5{ I )

C(3)

0.334( I )

0.423( I )

1.2114(8)

5( I )

C(4) C(51 C(6) C( 7 ) C(81 C(9) C(10) C( I I )

0.246( I I 0.157( I ) 0.156( I ) 0.246( I ) 0.065( I ) 0.010( I ) 0.546(I) 0.462( I )

0.389( 0.455( 0.554( 0.589( 0.418( 0.267( 0.747( 0.903(

1.2537(8) 1.3156(8) 1.3278(91 L2852(9) 1.3693(81 1.414( I ) 1.171(I) 1.2739(9)

5( I ) 5( I ) 6( I ) 6( I ) 5( I ) 8(2) 6(I) 5( I )

C(12) C(13)

0.396( I ) 0.361(I)

0.891 ( 1) 0.971(I)

1.3526(81 1.4074(8)

5{ I ) 5(I)

C(14) C(151 C{ 161 C(17)

0.391 ( I ) 0.453(I) 0.488( I ) 0.357( 1 )

1.060( I ) 1.072(I) 0.996( 1 ) I. 146( I }

1.3846(8) 1_'1063(91 1.2503(91 1.4442(8)

5( 1 ) 6111 6{ 1 ) 5( 1 )

I) 1) I) I) I) I) I) I)

C( 18)

0.249( I )

1.209( I )

1.577( I )

8(2)

C(19) C(20) C(211 C( 221 C(231 C(24) C( ~ ) C(26) C(271 C(28) C(29)

0.717( I ) 0.8061 I ) 0.747( I i 0.776( I I 0.8611 I) 0.922(I) 0.895( I ) 0.883( I ) 0.9~'t(21 0. ';; ,( I ) 0.8a9( I )

0.700( I ) 0.816( I ) 0.932(I) 1.002( I ) 0.961(I) 0.845(I) 0.774( 1 ) 1.046( I ) 1.071(I) 0.515( I ) 0.350( I I

1.0412(8) 0.9338(8) 0.9397(8) 0.8768(9) 0.8078(8) 0.8049(8) 0.8677( 81 0.738( I ) 0.609( I I 1.0358(9) 0.951918)

5( I ) 5( I ) 5(I) 5( i ) 5(I) 6(I) 6( I ) 6( I ) 10(21 5( I ) 5( I )

C(30) C( 31 ) C( 32l

0.950( 1) 1.039( I ) 1.036( 1)

0.366(I) 0.277( I ) O.175( I )

0.8982(8) 0.8592(9) 0.8732(8)

6(I) 6( I ) 6( I )

C(33) C(34) C(351 C(36)

0.942(I) 0.854( I I 1.134(I) 1.208(21

0.161(I) 0.249( I ) 0.075(2) -0.110( I )

C(37)

0.686( I )

0.255( I )

0.398( I )

7.6(4)

C(38) C(39) C(401

0.592( I ) 0.424( 21 0.3181 I )

0.325( I ) 0.425(I) 0.470( 1 )

0.339( I ) 0.569(I) 0.525( I )

7.9(4) 9.0(4) 8.3(4)

0.928(I) 0.9684(9) 0.829(I) 0.797( I )

7(I) 6( 1 ) 7(21 12(2)

structure of 4 are distorted from linearity in a very peculiar curved fashion. The curvature does not involve any strongly distorted bond angles, it is the cumulative result of small

166

M.E. Squires. A. Mayr / hu~rganica Chimica Acta 264 (1997) 161-169

Table 4 Final atomic coordinates and B,.q values of complex 5

Table 5

Atom

.~

y

z

B,,~

Ill) lad( I ) O( I ) 0(2) N( I ) C(I) C(2) C( 3 ) C(41 CI5) C(6) C(7) C(81 C{9)

0.28632(3) I/2 0.2009(4) -0.0958(4) 0.3813(5) 0.4273l 5) 0.308515) 0.4310{ 5 ) 0.3547(51 0.1598{51 0.0421 (5) 0.1149(51 0.0723(5) 0.1329(81

0.83882(31 I/2 0.1806(4~ 0.2291(41 0.3777(4) 0.4211(51 0.3330(51 0.2842( 51 0.2470(5) 0.2568(5) 0.3038(5) 0.3425(5) 0.2209(5) 0.1403(81

0.42417(3) 1/2 -0.1779(31 -0.0198(31 0.2962(3) 0.3705(4) 0.2085(4) 0.0789(4) -0.0070(41 0.0379(4) 0.1694(41 0.2565(4) - 0.0544(4l -0.2743(5)

4.01(21 2.86(3) 4.8(3) 4.9(31 3.8(3) 3.5(3) 3.2(3) 3.5 ( 31 3.5(3) 3.0(3) 3.4(31 3.6(3) 3.6(3) 6.2(6)

- - ~

Fig. I. (a) Molecular structure of complex 3b. (b) View of a layer of molecular units in the crystal structure of 3b.

( a ) Selected bond lengths (,g,) for complex 3b FeI-II 2.6384(3) FeI-CI FeI-CI 1 1.862(4) OI-C8 OI-C9 1.468(5) O2-C8 O3-CI8 1.325(51 O3--C 19 O4-CI8 1.197(41 NI-CI NI-C2 1.396(41 N2-CI 1 N2-CI 2 1.409(41 C5-C8 CI5-CI8 1.492(41

1.860(41 1.329(6) 1.191(5) 1.454(41 1.150(5) 1.149(41 1.491 (5)

( b ) Selected bond angles (°) for complex 3b lI-Fel-ll 180.00 II-FeI-CI II-Fel--CI I 87.3( 1 ) CI-FeI-CI CI--Fel--C 11 88.2( 1 ) CI I-Fe I-C 11 FeI-CI-NI 176.9(41 FeI-CI I-N2 CI-NI--C2 168.9(4) CI I - N 2 - C I 2 OI-C8-O2 124.8(41 O3-CI8-O4 O2-C8--C5 124.1(51 O4-CI8-CI5

87.6(11 180.00 180.00 176.0(3) 164.3(41 124.4(41 123.6(41

( c ) Selected bond lengths ( A,) lbr complex 4 Col-I I 2.87913) Col-12 CoI-CI 1.87( I CoI-CIO Co I-C 19 1.86( I Co I-C28 Oi~C8 1.18( I O2-C8 O2-C9 1.45( I O3-C 17 O4-C17 1.33(I O4-CI8 O5-C26 I. 18( I O6-C26 O6--C27 1.43 { 11 O7-C35 O7-C36 1.4312 ) O8-C35 NI-CI 1.13( 1 I NI-C2 N2-CI0 1.18( 1 ) N2-CI I N3-CI9 1.14( I ) N3-C20 N4-C28 I. 15( I ) N4-C29 C5-C8 1.50( 2 ) C 14-C 17 C23-C26 1.50( 2 ) C32-C35

2.838(3 I 1.82( 1 ) 1.85 ( I ) 1.32(21 1.19( I 1 1.42(21 1.33(2) 1.31 ( 2 ) 1.21 ( 2 ) 1.41( I ) 1.42(2) 1.40{ 1 ) 1.42 ( 21 1.48 ( 2 ) 1.52(2)

(d) Selected bond angles (°) for complex 4 11~2o1-12 171.95(61 ll~Sol-CI II-CoI-CI0 91.8(41 ll-CoI-Cl9 I I - C o I-C28 94.0( 4 ) 12-Co 1421 12~oI-CI0 90.8(4) 12-Coi-C19 12~So 1-C28 83.0(4 ) C I-Co I-C I0 C I-CoI-CI9 172.8(5 ) C l-Co I-C28 CIO-CoI-CI9 89.8(5) C 10-Co1-C28 CI9-CoI-C28 87.8( 51 CoI-CI-N I Co 1-C28-N4 174( I 1 C o t - C 10-N2 CoI-CI9-N3 172( I ) C I - N I-C2 CI0--N2-CI I 177( 1 ) CI9-N3-C20 C28-N4-C29 172{ I ) OI-C8-C5 01-C8-02 125{ I ) 03-C17-CI4 O3-C 17-O4 123 { 11 O5-C26-C23 O5--C26-O6 125 ( I ) O8-C35-C32 O7-C35-O8 124( I )

91.5(41 81.4(41 96.2 ( 4 ) 91.0(41 89.4( 5 ) 93.8(5 ) 173.3{6) 1771 I ) 178 ( I ) 178( I ) 166( I 1 123( 11 124( 11 123111 I 19( 2 )

( e ) Selected bond lengths ( 3, ) tot counplcx 5 Pd 1-11 2.5902( 8 ) Pd I-C I OI-C8 1.321 (5) OI-C9 O2-C8 1.2{)3( 41 N I-C I N I-C2 1.410( 4 ) C5-C8

1.956(4 ) 1.439{ 51 I. 136*,41 1.495( 5 )

consecutive bends across the entire length of the isocyanide

II-PdI-CI

¢f) Selected bond angles (°) for complex 5 11-Pd I-I I 180.00 C I-Pd I-C I

89.5(I)

180.00

ligands. The molecular structure of 5 is unexceptional. In the crystal, the linear molecules are neatly packed in layers as shown in Fig. 3(b). The shortest intermolecular distances

CI-NI-C2 01-c8-c5

175.3(41 112.0(3)

116.6(3) 123.6(31

PdI-CI-NI

C8-OI--C9 02--c8-c5

178.6(3)

M.E. Squires, A. Mayr / Inorganica Chimica Acre 264 (1997) 161-169

167

o5 08

~ 4 ~

~

C16

.,-,P • o,o-~,~c.

(b) Fig. 3. {a) Molecularstructureof complex 5. (bt Smallsectionof a layer of molecularunits.

c=~

~,,~ v,

(a)

Fig. 2. (a) Molecular structure of complex 4. Ib;~ Two views of a row of

molecularunits. between the methylbenzoate groups are in the range 3.3-3.5 A. Alkylbenzoate groups are not among the ¢rstacking groups frequently used in molecular self-assembly processes [201. Nevertheless, their interactions appear to cor~tribute in a decisive manner to the creation of the intriguing solid state structures of 3b and 4. This would suggest that isocyanide metal complexes with specifically designed ¢r stacking ligands could be of potential interest as building blocks for the selfassembly of complex solid state stn!ctures, lntermolecular or-or contacts also exert a dominant influence in the crystal structure of the complex [Pdh(CN-3-quinolyl):l [51. After having synthesized complexes 2-5, we were interested in testing whether the alkoxycarbonyl groups could be subjected to functional group transformations. In this context, it is necessary to pay attention to the potential reactivity of the coordinated isocyanide groups [ 1,9l. It is well documented that metal centers with low electron density, i.e. metals in medium to high oxidation states, activate isocyanide ligands rewards attack by nucleophiles [ 1,22]. At the same

time, however, the isocyanide functionality in such systems is extremely resistant towards electrophiles [ 23 ]. Activation of isocyanide groups towards attack by electrophiles is only successful in metal complexes with high electron density, e.g. Iow-valent complexes of the early transition metals [ !,24[. In most ordinary isocyanide metal complexes, the coordinated isocyanide group is unreactive towards e l e c t r ~ i l e s . Thus, significant ranges of electron density exist over which metal centers activate or deactivate i ~ y a n i d e ligands towards attack by electrophiles or nucleophiles, and L_h~ereis a reasonably wide range of electron density of metal centers, over which isocyanide ligands are inert to both ordinary electrophiles as well as nucleophiles. These guidelines concerning the reactivity and, more importantly in the p r e s t o context, the stability of isocyanide ligands are quite reliable for electronically and coordinafively saturated metal complexes. If electronically or coordinatively unsaturated complexes are involved, one also needs to be concerned about reactions initiated by attack at the metal center. In ge.qcim, however, the reactivity and stability of isocyanide ligands is straightforward to rationalize, and uadcr the proper conditions, many isocyanide racial complexes are thermally as well as chemically quite stable. This situation is of significant advantage as far as the development of robust molecular materials is concerned. Cationic cyclopentadieny! isocyanide iron( Ill complexes react easily with nucleophilic reagents such as amines, but are quite unreactive towards electrophiles [ 25 ]. We therefore sought to subject the alkoxycarbonyl group of complexes 2 to simple electrophilic functional group wansformations. Sequential treatment of complex 2b with BBr3 [26] and methanol was expected to lead to the formation of complex 2a. This outcome was confirmed by speclroscopic means ( IR and H ~ NMR), although the reaction was no~ sufficiently clean for the isolation of pure 2a. Auempts m achieve transformations of the alkoxycarbonyl groups in complexes 3 have also not led to well-defined results, primarily due to a low reactivity of the ester groups. It was found, for example, that 3a withstands treatment with HCI/H:O in CH:CI: and exhib-

168

M.E. Squires. A. M a y r / htor, eaniea Chimico Acta 264 ¢19971 161-169

its little r e a c t i v i t y t o w a r d s p i p e r i d i n e in THF. in both c a s e s o v e r p e r i o d s o f several d a y s 4. W h i l e these p a r t i c u l a r e x p e r i m e n t s h a v e been u n p r o d u c t i v e , the lack o f r e a c t i v i t y i m p l i e s that the i s o c y a n i d e functionalities in c o m p l e x e s o f type 3 are d e a c t i v a t e d t o w a r d s attack by e i e c t r o p h i l e s as well as n u c l e o p h i l e s . In contrast to o u r results, base h y d r o l y s i s o f the e s t e r g r o u p in I Re(N(CH_~CH_,S)3) ( C N C H 2 C O 2 E t ) l has r e c e n t l y been d e m o n s t r a t e d by Hahn and c o - w o r k e r s I 1 0 g l .

4. Conclusions

Several transition metal i s o c y a n i d e c o m p l e x e s c o n t a i n i n g a l k o x y e a r b o n y l g r o u p s have been synthesized. The structural studies o f selected e x a m p l e s reveal that a r y l i s o c y a n i d e metal c o m p l e x e s can form intricate m o l e c u l a r solid state structures b a s e d on e v e n w e a k i n t e r m o l e c u l a r 7r s t a c k i n g interactions. P r e l i m i n a r y a t t e m p t s c o n c e r n i n g selective t r a n s f o r m a t i o n s o f the e s t e r g r o u p s o f the c o o r d i n a t e d i s o c y a n i d e l i g a n d s have, unfortunately, been unproductive. The reason for this outc o m e has been p r i m a r i l y a lack o f reactivity o f the s i m p l e a l k o x y c a r b o n y l g r o u p s rather than the potential r e a c t i v i t y o f the metal i s o c y a n i d e entities. Thus the results s u g g e s t that w i t h o n l y s l i g h t l y more reactive ester or other functional groups, the general strategy, w h i c h p r o m p t e d this study, s h o u l d b e c o m e feasible. T h i s has i n d e e d been d e m o n s t r a t e d by u s i n g f o r m y l - s u b s t i t u t e d a r y l i s o c y a n i d e m e t a l c o m p l e x e s I271.

5. Supplementary material

Further details o f the crystal structure i n v e s t i g a t i o n s of c o m p l e x e s 3b, 4 and 5 may be o b t a i n e d from the autilors.

Acknowledgements

W e thank Professor Stephen A. Koch and D a v i d N e l l i s for d e t e r m i n i n g the crystal structures. F i n a n c i a l support by the D o n o r s o f the P e t r o l e u m R e s e a r c h Fund, a d m i n i s t e r e d by the A m e r i c a n C h e m i c a l Society. and by the National S c i e n c e F o u n d a t i o n is g r a t e f u l l y a c k n o w l e d g e d .

References

I I I (al L. Malatesta and F. Bonati. Isocvanhh, Comph,xes e~l Transition Metals. Wiley. New York. 1969; ( b ) P.M. Trcichel. Adv. Organomet. Chem.. II { 19731 21: (el Y. Yamamoto. Coord. Chert1. Rev.. 32 ( 1980 ) 193; t d ) E. Singletou and H.L Ousthuizen. Adv. Organemtet. Chem,. 22 ( 19831 2119: (e) F.E. Hahn, Angen'. Chem., 105 ( 19931 681 : Aneen'. Chetn.. hit. I'-tL Engl., 32 { 19931 65n. For tile aminoiyr,is of ~l-i~ocyanoacetic esters to aflbrd amides of the type CNCHRCONHR'. see Rcf. 18e ].

121 (a) I. Feinslein-Jaffe. F. Frolow. L. Wac}:e,-le,A. Goldman and A. Efraly, J. Chert1. Sot., l)alum Trans., ( 19881 469: ~ ) M, Hanaek. S. Deger and A. Lange, Coord. Chem. Rev., 83 { 1988) 115. 13 ] ( a ) J.-M. Lehn, Stq~relmoh,eular Chemistry. VCH, Weinheim, 1995: (b) J.C. MacDonald and G.M. Whltesides, Chem. Rev,, 94 ( 19941 2383: (c) D.S. Lawrence. T, Jiang and M. Levett, Chem. Rev., 93 119951 2229. [4] L.-F. Mao and A. Mayr. hlorg. Chem., 35 ( 19961 3183. [ 5 ] L Gum and A. Mayr, hu~rg. Chin1. Acre. 261 ( 1997 ) 141. 16 ] (a) Y.-L Chang, M.-A. West. F.W, Fowler and J.W. Lauhcr, J. Am. CTlem. Sot,, 115 (1993) 5991: (b) S.J. Geib, C. Vicent, E. Fan and A.D. Hamilton, Angew. Chem.. 105 (1993) 83: Angew. Chem.. hit. Ed. Engl.. 32 ( 19931 119: (c) X. Wang, M. Simard and J.D. Wuest. J. Am. Chem. Soe.. 116 ( 19941 12119: (d) S. Hanessian. M. Simard and S. Roelens, J. Am. Chent. Sot.. I 17 ( 1995 ) 7630; (e) K. EichhorstGerner, A. Stabel. G. Moe~sner, D. Declerq, S. Valiyaveettil, V. Enkelmann, K. Miillen and J.P. Rabe, An¢eu'. Chem., 108 ( 19961 1599: Angew. Chem.. Int. Ed. Engl.. 35 ! 19961 1492. 171 {a) I. Ugi. U, Fetzer. U. Eholzer, H. Knupfer and K. Offermann, Angew. Chem., 77 119651 492: (b) C. Grundmaon, Methoden Org. Chem. (Hottben WeylJ, Vol. E5.4th edu.. 1952-1985, p. 1611. ] 8 ] (a) W.P. Fehlhammer, K. Bartel. B. Weinberger and U. Plaia. Chem. Ber.. / 18 ( 1985 ) 2220: ~b ) D Samuel. B. Weinraub and D. Ginsburg, J. Org. Chem., 21 ( 19561 376:(¢1 R. Bossio. S. Marcaccini and R. Pepino, Liehigs Ann. Chem.. ( 19901935: ( d ) K. Gollnick, S. Koegler and D. Maurer. J. Org. Chem.. 5711992 ) 229:1 e ) K. Matsumoto, M. Suzuki. N. Yoneda and M. Miyoshi, .~vnthesis, 119771 249. 191 W.P. Fehlhammer and M. Fritz, Chem. Rev.. 9,¢ ( 19931 1243. I In l {a) W. Beck, W. Weigand. U. Nagel and M. Schaal. Angew. Chem.. 96 (1984) 377: Angew. Chem., Int. l:'d. Engl., 23 ( 19841 377; (h) G.J, Baird and S.G. Davies. J. Orgammwt. Chem., 262 ( 19841 215: 1c1 E, Bar, W.P. Fehlhammer, W. Weigand and W. Beck. J. Orgttnomet. Chetll., 347 { 1988 ) 101; ( d ) M. Schaal, W. Weigand. 13. Nagel and W. Beck. Chem. Bee., I1,~ { 19851 2186: (e) W. Weigand, U. Nagel and W. Beck. Chem. Bee., 123 ( 19901 439; (f) F.E. Hahn, M. Tamm and T. Liiggcr. Angew. Chem., 106 119941 1419: Angew. Chem., hit. Ed. EngL. 33 { 19941 1356: (g) M. Glaser, H. Spies. T. Lugger and F.E. Hahn, J. Organomet. Cllem., 50,'1 ( 1995 ) C32. 111} (a) T. Kaharu, R. Ishii and S. Takahashi. J. Chem. Soe.. Chem. COtlIIIIUII., ( 19941 1349: (bl T. Kaharu, T. Tanaka. M. Sawada and S. Takahashi, J. Chem. Mater., 4 { 19941 859. 1121 R.B. King and M.B. Bisnette, J. Am. Chem. Sot'.. 86 ( 19641 1_~67. 1131C.W. Huffmann. J. Otzt~.Chem.. 23 119581 727. 1141 S. Lincoln and S.A. Koch, huJrg. Chem.. 25 ( 19861 1594. 1151 N. Walker and D. Stuart, Acta CO'stallogr.. Sect. A. 39 ( 19831 158. [ 161 Singh, Crystal Strut lure Amtlwis St~lht'are. Version 1.6, Molecular Structure Corporation, The Woodlands, TX. 1993. 1171 K.K. Ioshi, P.L. Pauson and W.H. Stubbs, J. Orgammwt. Chem.. I ( 19631 51. [ [81 L. Malatesta. A. Sacco and G. Padoa, Am1. (-Tlim. fltaly). 43 ( 19531 617. I 191 ( a ) L. Malate~,taand A. Sacco. Gaz:. Chim. Ital.. 83 ( 1953 ) 499: (h) C.J. Gilmore. S.F. Watkins and P. Woodward. J. Chem. Soe, A, 11969 ) 2833: {c) D. Baumann. H. Endres. H.J. Keller, B. Nu{~erand J. Weiss, At'tit ('r.vslalhJgr.. Sect. B, 3/( 1975 ) 41); ( d ) F.E. Hahn and T. Liigger, J. O~anomet. Chem.. 481 { 19941 189. 121}I ~a ) M. Angoletta. Ann. Chim. ¢lttt(v). 45 { 1955 ) 9711:{b ) N.A. Bailey. N.W. Walker and J.A.W. Williams. J. Organomet. Chem.. 37 { 1972 ) C49: (c) C.-M. Che, [:.H. Herbstcin. W.P, Schaefer, R.E. Marsh and H.B. Gray, htorg. Chem., 23 ( 19841 2572. 121 I (a) D.B. Amabilino and J.F. Stoddart. (Twin. Rev.. 95 ( 1995 ) 2725: {b) C.A. Hunter and J.K. Sanders. J. Am. (-Twin. Soc. 112 119901 5525: ~c~ G,R. Desiraju. Tile Cryst, I as a Sul~ramoh'('uhtr EntiO'. Wiley. New York. 1995.

M.E. Squires, A. Mayr / hu~eaniea Chhnica At'ut 264 ¢1')971 161-169 122 ] ( a ) E.M. Badley. J. Chart, R.L. Richards and G.A. Sim. J. Chem. Sot'.. Chem. Commun.. (1969) 1322: Ib) E. Rotondo. M. Cusamano. B. Crociani. P. Uguagliati and U. Belluco. J'. Organomet. Chem.. 134 11977) 249. 1231 W.Z. Heldt. J. Org. Chem.. 2711962) 2604. 1241 t a ) J. Chart. A.J.L. Pombeiro. R.L. Richards, G. Royston. K. Muir and R. Walker. J. Chem. Sot.. Chem. Commun.. (1975) 71)8: (b) A.J.L. Pomheiro and R.L. Richards. Coord. Chem. Rev.. 104 119901 13: ( b )

169

S. Warner and S.J. Lippard. Or~anometallic.~. 8 ~ 19891 228: Icl A.C. Filippou and W. GrUnleitner. J. Organomet. Chem.. 3981 It)901 99. 1251 ( a ) W.P. Fehlhammer. A. Mayr and C. Giilz..I. Organomet. Chem,. 209 11981 I 57: I b ) F.E. Hahn and M. Tamm. J. Chem. Sot.. ~ 1995 ) 569. [ 261 A.M. Felix. ,/. Ore. Chem.. 39 11974 ) 1427. 1271 K.Y. Lau. A. Mayr and K.K. Cheung. in preparation.