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Structure of and Bonding in an Alkyne-Nonacarbonyltriiron Complex. A New Type of Iron-Acetylene Interaction John F. Blount,lalbLawrence F. Dahl,'",' Cornelis Hoogzand,ld and Walter HubelId
Contribution f r o m the Department of Chemistry, University of Wisconsin, Madison, Wisconsin, und Union Carbide European Research Associates, Brussels, Belgium. Received August 20, 1965 Abstract: Complexes of the class RC2R'Fe3(CO)9,isolated in small yields along with other organoiron carbonyl complexes f r o m the reaction of diphenylacetylene with F e 2 ( C 0 ) 9and methylphenylacetylene with Fe3(C0)12,have been characterized both by physical a n d chemical means including a three-dimensional single-crystal X-ray study of the diphenylacetylene derivative. Crystals of CSH5C2C6H5Fe3(C0)9 are triclinic with t w o molecules in a unit cell of symmetry P i a n d o f reduced cell parameters a = 9.08, b = 9.16, c = 16.28 A., a = 80" 15', p = 75" 57', y = 62" 31 '. A full matrix isotropic least-squares refinement of the structure yielded discrepancy factors of R1= 8.6 a n d R2 = 9 . 2 z . T h e idealized molccular configuration h a s C,-m symmetry a n d consists of a n isosceles triangle of iron atoms with three terminal carbonyl groups attached t o each iron a t o m . T h e diphenylacetylene g r o u p is stereochemically disposed above the plane of iron atoms such that o n e acetylene carbon is coordinated to all three iron atoms while the other acetylene carbon is bonded t o the two symmetry-related iron atoms. A qualitative bonding description of this new type of metal-acetylene interaction consistent with the molecular parameters a n d the diamagnetism of the c o m p o u n d is given in terms of the functioning of the acetylene as a metal-coordinating olefinic g r o u p by the formation of o n e two-center a n d two three-center bonds. T h e reactions a n d stereochemical implications o f this triiron-alkyne complex, regarded as o n e of the intermediates in the formation of other organoiron carbonyls with m o r e complicated ligands, are discussed.
R
of alkynes with F e ( C O ) j , F e 2 ( C 0 ) 9 , and Fe3(CO)12have yielded a wide variety of organoiron carbonyl complexes w i t h unusual c o n f i g u r a t i o n s and novel t y p e s of One such complex, p r e p a r e d in low yields from t h e r e a c t i o n of d i p h e n y l a c e t y l e n e w i t h F e z ( C 0 ) 9 at room t e m p e r a t u r e for s e v e r a l days, is a d i a m a g n e t i c c o m p o u n d of formula C6Hjeactions
new t y p e o f interaction involving an a c e t y l e n e coord i n a t e d with t h r e e metal atoms w h i c h c a n n o t be simply d e s c r i b e d by t h e usual a-7r-bonding f o r m u l a t i o n . Experimental Section
Preparation and Properties of C6HjC2C6HjFe3(CO)o,A suspension of 72 g. (0.2 mole) of Fe2(C0)gin 0.5 I. of light petroleum C2C6HjFe3(C0)9. T h e corresponding methylphenylether was stirred at room temperature, and ten portions each of 1.78 a c e t y l e n e i r o n c a r b o n y l c o m p l e x , C H 3 C 2 C 6 H 5 F e 3 ( C 0 ) 9 , g. (0.01 mole) of diphenylacetylene were added at intervals of 5 hr. p r e v i o u s l y was i s o l a t e d * f r o m the r e a c t i o n of Fe3(CO)12 The filtered reaction mixture was evaported to dryness under reduced pressure in order to eliminate the Fe(CO), formed. The w i t h m e t h y l p h e n y l a c e t y l e n e a t 90" a n d i n c o r r e c t l y complex, C&C2C&Fe3(CO)g, was extracted with petroleum when no f o r m u l a t e d at first2 as CH3C2C6H5Fe2(CO)lo ether from the residue consisting mainly of [(C6HjC2C6Hj)2CO]oxygen a n a l y s i s was available. The i n f r a r e d s p e c t r a F e ~ ( C 0 ) 6and ~ some (C6HjC2C6Hj)2Fe2(CO)63,and the filtrate was of b o t h t h e d i p h e n y l - a n d m e t h y l p h e n y l a c e t y l e n e d e r i v a chromatographed on silica gel. The complex together with some unreacted diphenylacetylene was eluted with petroleum ether. Retives show a b s o r p t i o n bands c h a r a c t e r i s t i c of t e r m i n a l crystallization from petroleum ether or petroleum ether-benzene carbonyl groups only. mixtures yielded 0.6 g. (1 %) of black needles which decompose at Since c o m p l e x e s of formula R C 2 R ' F e 3 ( C 0 ) 9 p r e 147" without melting. s u m a b l y a r e i n t e r m e d i a t e s in the f o r m a t i o n of organoAnal. Calcd. for C23H10Fe309:C, 46.20; H, 1.69; Fe, 28.02; iron c a r b o n y l s with more c o m p l i c a t e d Ligands their 0 , 24.09. Found: C, 46.09; H, 1.69; Fe, 27.80; 0, 24.26. C6HjC2C6H6Fe3(C0)9is diamagnetic with ~ ~ ~ =1 s t e r e o c h e m i s t r y is o f p r i m e significance. A t h r e e d i m e n s i o n a l X-ray a n a l y s i s of C ~ H ~ C Z C ~ H ~ F ~ ~ ( (-131.5 C O ) ~ , 3.0) x lO-6~m.3mole-~. TheinfraredspectruminKBr shows bands at 2083 (m) and 2024 (s) with shoulders at 2000, h e r e d e s c r i b e d , has e s t a b l i s h e d t h e m o l e c u l a r c h a r a c t e r 1976. and 1957 cm.-1. Its n.m.r. spectrum (60 Mc.) in CS2 conof t h e c o m p o u n d and h a s r e v e a l e d t h e existence of a sists of three groups of resonances for the phenyl protons centered at -7.3, -6.8, and -5.9 p,p,m. (relative to Si(CH&) with an in(1) (a) University of Wi\consin; (b) National Science Predoctoral tensity ratio of 5 :3 :2. The different chemical shifts of the ortho Fellow, 1962-1964; the X-ray work is abstracted in part from the Ph.D. protons (-5.9 p,p.m.) and the rneta andpara protons (-6.8 p.p.m.) thesis of J. F. Blount, Univcrsity of Wisconsin, June 1965; (c )Alfred P. Sloan Research Fellow; (d) Union Carbide European Research of one phenyl group from the five protons of the other phenyl Associates. group may perhaps be explained more readily by a diamagnetic ( 2 ) W. Hiibel, E. H. Braye, A. Clauss, E. Weiss, U. I
