Primary alkenyl phosphine complexes of chromium and molybdenum;synthesis and characterisation of tricarbonyl( 1,5,9-triphosphacyclo-dodecane)chromium(o)Peter G . Edwards,* James S. Fleming, Sudantha S. Liyanage, Simon J. Coles andMichael B. HursthouseDepartment of Chemistry, University of Wales Card$$ PO Box 912, Cardiff CFI 3TB, UKThe reaction offac-[Cr(CO),(MeCN),1 with primary allyl- and vinyl-phosphines gave rise to thecorresponding tris(primary phosphine)chromium tricarbonyl complexes. Radical-catalysed coupling of the allylfunctions with PH groups in the tris(ally1phosphine) complex led to the chromium tricarbonyl complex of 1,5,9-triphosphacyclododecane. The molybdenum analogue of the chromium prop-2-enylphosphine complex has alsobeen prepared. Radical-catalysed coupling of the vinyl functions with PH groups in these complexes resulted innew complexes with multidentate ligand systems but not in complexes of new macrocycles.The crystalstructures of the new 1,5,9-triphosphacyclododecane and prop-2-enylphosphine complexes have beendetermined and structural implications for these template cyclisation reactions investigated.We have an interest in acyclic tridentate systems includinglinear triphosphines for the following principal reasons. Thesecompounds have the ability kinetically to stabilise unusualchelate complexes which may also exhibit dynamic solutionbehaviour. As well as forming chelate-stabilised complexes withpendant donors available for further stabilisation of lower-co-ordinate reaction intermediates, they can support bimetallicand polynuclear complexes, acting as bridging ligands.Theyalso have the ability to co-ordinate facially to three mutually cissites on a metal which is of considerable interest in the studyof new properties and in applications of transition metals incatalysis. In this last property they act as six-electron ligandsand can be considered analogous to the cyclopentadienyl familyof ligands. Their co-ordination versatility complicates the studyof their complexes however, and restricts their application. Inorder to achieve a higher degree of control of the co-ordinationbehaviour of such tridentate systems triphosphorus macrocyclesare of interest. Again, in order to simplify the co-ordinationchemistry, we have chosen to investigate triphosphorusmacrocycles for which mixtures of isomers is restricted andhence where the bridging 'backbone' functions betweenadjacent phosphorus atoms are identical.Such compounds arevery rare; prior to our current study, there was only oneexample of a 1,5,9-triphosphacyclododecane complex reportedby Norman and co-workers' who also prepared the 1,6,11-triphosphacyclopentadecane analogue, both of which wereprepared by a metal-template route with the added benefitof control over the stereochemistry at phosphorus. We haveextended this chemistry to tungsten and have recently reportedthe syntheses and characterisations of the first complexesof tritertiary derivatives of 1,5,9-triphosphacyclododecane.The free, unco-ordinated macrocycles are currently unknowndespite attempts at their liberation from the metal templateupon which they were prepared.Since the co-ordinationchemistry of phosphorus-containing macrocycles of thesetypes, as well as the reaction chemistry of complexes andorganometallic derivatives, will be of interest, we have chosento extend this study to similar chromium complexes withthe aim of broadening our knowledge of these macrocyclicphosphorus systems. In this way we hope to maximise ouropportunities for the design of synthetic procedures to the freetriphosphorus macrocycles. In addition, since the templatecyclisation works well for propenyl- and butenyl-phosphines,generating the corresponding twelve- and fifteen-memberedmacrocycles, we have also investigated the preparation ofsimilar vinylphosphine complexes and their coupling reactions.Results and DiscussionSynthetic routes to the new compounds discussed below arecollected in Schemes 1-3, NMR data are in Table 1 and IR andanalytical data in Table 2.Chromium allylphosphine and macrocycle complexesThe synthetic approaches to the molybdenum and tungstencyclo-triphosphine complexes are similar uia the tris(ally1phos-phine)tricarbonyl complexes. These were prepared by reactionof the tricarbonyl(mesitylene)metal(o) complexes with allylphos-phine (M = Mo 1; or W 2).Tris(ally1phosphine)tricarbonyl-chromium(0) 3, however, could not be prepared from tricar-bonyl(mesitylene)chromium(o) cleanly and in good yield.Analternative route (Scheme I) uia the substitution of aceto-nitrile in tris(acetonitrile)tricarbonylchromium(o) by allylphos-phine gives rise to the required tris(phosphine) complex in highyield and this route is also applicable to the molybdenum andtungsten analogues. By this reaction, tris(ally1phosphine)tricar-bonylchromium(o) was obtained as a viscous yellow oil whichwas characterised spectroscopically. Thus the co-ordination ofallylphosphine is clearly indicated by 'P NMR spectroscopy(6 -23.6, t, 'JpH = 320 Hz) where the co-ordination chemicalshift (A3'P = 6co-ordinated - &nco-ordinaled p) relative to thefree phosphine ligand is ca. 1 1 1 ppm and ' JPH increases by ca.125 Hz. The increase in 'JpH is similar to that observed forthe molybdenum and tungsten analogues 1 and 2 (Table l),although A3 'P increases markedly with decreasing atomicnumber of the metal atom in this series.In the 'H and ' 3C-('H}NMR spectra resonances due to allyl functions are observedand the spectra are very similar to those for the analogues 1and 2. In the IR spectrum two bands assigned to v(C0) (1932,1834 cm-') confirm the fac-octahedral geometry and otherexpected characteristic ligand absorptions were observed, i. e.v(PH) (2305 cm-') and v(C==C) (1630 cm-'). The molecularion is also observed in the mass spectrum (m/z 358) as wellas fragmentation due to loss of allylphosphine and carbonylligands.J. Chem. SOC., Dalton Trans., 1996, Pages 1801-1807 1804 16R3 7Scheme 1phosphine (3 : l), CH,CI,; (iii) aibn, 80 "C(i) Allylphosphine (3 : I), CH,CI,; (ii) vinyl- or prop-Zenyl-When solutions of complex 3 in toluene are heated (8&100 "C) with aibn (azobisisobutyronitrile), a new material 4 canbe obtained upon work-up as colourless crystals in good yield(cu. 80%).Microanalysis indicates the formula C,H, iP3-Cr(CO), and spectroscopic data clearly confirm that the allyl-phosphine functions have coupled to give rise to the new1,5,9-triphosphacyclododecane chromium complex (Scheme 1).Thus in the ,'P NMR spectrum a doublet is observed (6 -3.9,'JpH = 331 Hz) consistent with a secondary phosphine; thedownfield shift upon cyclisation [relative to the tris(alkeny1-phosphine) precursor] is similar to the behaviour of themolybdenum 5 and tungsten 6 analogues and again a significant(monotonic) increase in S(,'P) occurs as the atomic number ofthe metal atom decreases.The 'H and 13C-{1H} NMR spectraare also very similar to those of 5 and 6; there is little variationin 6(CO) between the tris(alkeny1phosphine) precursors and thecorresponding macrocycle complexes. In the mass spectrum anintense molecular ion is observed (M', m/z 358, 62%) alongwith a fragmentation pattern indicating sequential loss ofcarbonyls. Two carbonyl stretching absorptions appear in theIR spectrum [v(CO) 1918,1820 cm-'1 which are consistent witha fuc-tricarbonyl octahedral structure. A band assigned tov(PH) (2298 cm-') and the absence of a band due to v ( M ) arealso consistent with the formation of the macrocycle.Thelowering of v(C0) relative to that of 3 is similar to variationsobserved in the molybdenum and tungsten analogues and mayindicate that the secondary phosphine donors in the macro-cyclic ligand are poorer x: acceptors than the monodentateprimary phosphines, as might be expected.Vinylphosphine complexesIn order to investigate the viability of this template route to1,4,7-triphosphacyclononane derivatives, chromium complexesof vinyl- and prop-2-enyl-phosphine were investigated. Sincevinylphosphine is commonly contaminated with ethylphos-phine when prepared by reduction of vinyl phosphonates, thedetailed study was performed with prop-2-enylphosphine.The reaction of 3 mole equivalents of prop-2-enylphosphinewith [Cr(CO),(MeCN),] gives rise to pale yellow solutionsfrom which colourless crystals may be obtained in high yield bycrystallisation from light petroleum.Analytical data for thesecrystals indicate the composition, [Cr(CO),{ H,PC(Me)CH,),]7. Spectroscopic data are consistent with this formulation. Themolecular ion is observed in the mass spectrum (m/z 358) alongwith a fragmentation pattern indicating successive loss ofcarbonyl groups. In the IR spectrum two bands may beassigned to v(C0) (1 940, 1848 cm-') indicating afuc-octahedralarrangement of ligands and bands assigned to v(PH) (2298cm-') and v(C=C) (1 6 I6 cm-') confirm the presence of prop-2-enylphosphine ligands. The NMR spectra are also consistentwith 7 being the fuc-tris(primary phosphine) isomer since atriplet is observed in the ,'P spectrum (6 -12.8, 'JpH = 305Hz).The 'H and 13C-{1H} NMR spectra are also consistentwith magnetically equivalent phosphine ligands; resonancesassigned to alkene carbons are observed (6 134.7, 125.0) as areresonances due to the carbonyl (6 229.0) and methyl carbons(6 24.8).The tris(viny1phosphine) analogue of 7 , i.e. [Cr(CO),(H,P-CHCH,), J 8, may be prepared in a similar manner by additionof 3 mole equivalents of purified vinylphosphine to a solution of[Cr(CO),(MeCN),] and may be isolated as a pale yellow solid.Analytical data are consistent with the formulation and amolecular ion is observed in the mass spectrum (m/z 3 16). In theIR spectrum bands assigned to v(C0) (1939,1841 cm-'), v(PH)(2305 cm-') and v ( M ) (1602 cn-') are observed and againconfirm the presence of alkenylphosphine and a fuc-octahedralarrangement of carbonyl ligands. In the ,'P NMR spectrum theresonance due to co-ordinated primary phosphine appears as atriplet as expected (6 -29.3, 'JpH = 309 Hz) and alkenyl,carbonyl and PH functions are confirmed in the 'H and 13C-{ 'H} NMR spectra.The molybdenum analogue of complex 7 is readily preparedin the same manner by the addition of prop-2-enylphosphine to[Mo(CO)~(C,H,M~,-I ,3,5)] or to [Mo(CO),(MeCN),] andmay be isolated as pale yellow needles by crystallisation fromlight petroleum (b.p.40-60 "C). Analytical data are consistentwith the formulation [Mo(CO),{ H,PC(Me)CH,),] and thefac-tris(primary phosphine) structure is confirmed by spectro-scopic data.The 'P co-ordination chemical shift of the prop-2-enylphosphine ligands relative to free phosphine is much lessthan observed for the chromium compounds 7 and 8 (A = 76.4us. 108.6 and 107.2 ppm respectively). This effect was alsoobserved for the allylphosphine complexes 1 and 3 and appearsto be general for these primary phosphine complexes.Coupling reactions of tris(viny1phosphine) complexesAttempts to form triphosphacyclononane derivatives by cyclis-ation of the tris(prop-2-enylphosphine) complex 7 by thermal,radical or UV activation failed. In each case the reactionwas monitored by NMR ,spectroscopy and coupling wasobserved to occur although the expected product was not.Thus, heating a toluene solution of 7 in the presence of cata-lytic quantities of aibn (conditions identical to those for thesuccessful preparation of the triphosphacyclododecane complex4) generated a mixture of products with numerous peaks in the,'P-{ 'H) NMR spectrum.The predominant resonances weredue to secondary phosphines (doublets in the 31P NMRspectrum, 'JpH z 300 Hz) with poorly resolved fine structureand other peaks due to primary and tertiary phosphines werealso present, the latter indicating that intermolecular reactionsalso take place. These complex mixtures could not be readilyseparated and no pure components were identified. Furtherheating caused decomposition and precipitation of intractable,and presumably polymeric, materials. Thus, for the prop-2-enylphosphine complex 7 there appears to be a number ofreaction pathways operating under the conditions employed,presumably including intermolecular coupling (giving rise totertiary phosphines).However, there was no evidence ( 3 'P-{'H) NMR,3 in the range 6 +600 to -200) of vinylphos-phine - phosphaalkene tautomerism as had been observedfor [W(CO), { Me(H)PCHCH, )] upon heating under somewhatmore vigorous conditions than in the present case.4 Similar1802 J. Chem. Soc., Dalton Trans., 1996, Pages 1801-180Table 1 The NMR data for the metal-phosphine complexes 1-12891011126( 3 1P)O- 57.5 (t)-80.1 (t)-23.6 (t)- 3.9 (d)-32.1 (d)- 60.8 (d)- 12.8 (t)cis-[Cr(CO),( H,PC(Me)CH,) ,] -21.6 (t)CCr(CO),[H,PCH(Me)CH,P(H)C(Me)CH,}] 45.6 (dd),I5.0 (dt)JPHiHZ29531932033 131831230530930232 13 17, 320297A31P7754.4110.9---108.6107.276.4100.0-102&('H)b5.90, 5.10, 5.00 C X H3.92PH22.36 PCHz5.60, 5.10,4.90 C=CH3.50 PH,2.20 PCH,5.85, 5.10,4.95 C=CH4.05 PH,2.56 PCH,4.92 (m) PH1.95 (m) PCH,1.60 (m) PCH,CH,4.70 (m) PHI .80 (m) CH,4.82 (m) PH1.95 (m) PCH,1.70 (m) PCH,CH,5.50, 5.60 C=CH,4.65 PH,2.00 CH,6.28, 5.95, 5.80 C=CH,4.83 PH,5.50, 5.60 C=CH,4.60 PH,2.00 CH,5.70, 5.60 C S H ,4.75 PH,2.10 CH,5.60, 5.45 C-XH,4.65 PH, PH,2.12 C=CCH,2.00 CH1.80 CH,1.54CH35.85, 5.05,4.95 C=CH4.I0 PH,2.60 PCH,2.12 CH,S[ 13C-{ ' H}]217.7 CO135.4, 1 17.6 C=C26.4 PCH,21 7.9 (m) CO135.3 (s), 117.2 (s) C=C28.4 PCH, (d, 'JPc = 59 Hz)229 (m) CO135.2 (s), 1 17.8 (s) C=C26.5 (d, Jpc 59 Hz) PCH,230 (m) CO24.2 (d, 'Jpc 25 Hz) PCH,21.5 (m) PCH,CH,220 (m) CO25.0 (d, lJPc 38 Hz) PCH,22.9 PCH,CH,229 (m) CO134.7 (m) PC=C125.0 (m) PC=C24.8 (s)CH,229 (m) CO130.3 (m) PC=C125.5 (m) PC=C218 (m) CO134.8 (m) PC=C126.5 (m) PC=C24.8 (s)CH,223 (m) CO134.7 (m) PC=C126.3 (m) PC=C23.9 (s)CH,220.6 (m) CO135.8 (m) PC=C127.1 (m) PC=C24.9 (br m) CH,, CH5.4 (br m) CH,220.9 (m) CO135.8 (s) PC=C125.4 (s)CN1 17.2 (m) PC=C26.8 (m) PCH,21.1 (s) CH,a In CDCI, solution, relative to external H3P0, (85%).' In CDCI, solution, relative to SiMe,. ' In CDCI, solution, relative to solvent. Data fromref.1. ' Data from ref. 2. *JPp = 67 Hz.Table 2 Infrared spectroscopic" and analytical data for complexes 1-12IR/cm-' Analysis (%)Complex v(C0) v(PH) v(C=C) C H1'2 d345'6'789101112'1954, 18641935, 18251932, 18341918, 18201945, 18441910, 18251940, 18481939, 18411932, 18312066,2017, 1936, 18762073,2017, 1946, 18361911, 1883, 183422992350230522982305229823052298230523262333-163316301630---1616160216031623I632163035.7 (35.8)37.5 (40.2)39.5 (40.2)36.0 (35.8)28.5 (29.4)39.95 (40.20)33.90 (34.15)35.75 (35.80)37.45 (38.45)37.75 (38.45)35.40 (37.25)-Recorded in Nujol. Calculated values in parentheses. ' Data from ref. I . Data from ref.2. ' v(CN) at 2284 cm '.5.40 (5.25)5.40 (5.85)5.95 (5.85)5.40 (5.25)4.60 (4.30)5.80 (5.85)4.90 (4.75)5.20 (5.10)4.90 (4.50)4.70 (4.50)6.20 (5.90)-attempts to cyclise the vinylphosphine functions in 8 and the intractable materials. Again no evidence of vinylphos-prop-2-enyl functions in 9 resulted in similar observations. phine - phosphaalkene tautomerism was observed.Thus heating a solution of 8 in toluene in the presence of aibn Although the chromium(0) tris(phosphine) complexes areagain resulted in mixtures that gave rise to complex NMR not substitution labile at ambient temperature, in all these threespectra. Secondary phosphines could again be identified in both cases, during the early stages of the attempted cyclisations, freecases and continued heating resulted in the precipitation of unco-ordinated primary phosphine was generated in solutionJ.Chem. SOC., Dalton Trans., 1996, Pages 1801-1807 180and this may account for one of the undesirable competingreactions in this system, since any free primary phosphinewould readily enter into intermolecular coupling reactions.Thus the lability of phosphine ligands increases with increasingtemperature as might be expected and the cyclisation of theallylphosphine groups in 3 is rapid enough that dissociationdoes not compete detrimentally. No further variable-tempera-ture NMR behaviour was observed although in the formationof the chromium primary phosphine complexes evidence thatsuggests stepwise substitution of acetonitrile in [Cr-(CO),(MeCN),] was obtained from 31P NMR spectra of thereaction solutions where singlets assigned to mono(phosphine)-bis(acetonitrile), bis(phosphine)mono(acetonitrile) and thetris(phosphine) products were observed upon addition of prop-2-enylphosphine and allylphosphine (6 - 33.3, - 22.6, - 12.8and - 38.6, - 30.3 and -23.6 respectively).This is in contrastto the formation of the molybdenum tris(phosphine) analogueswhere only the desired tris(phosphine) complex is formed evenwhen a deficiency of primary phosphine is employed. Althoughthe chromium complexes appear to exhibit enhanced lability (incomparison to the molybdenum analogues), no attempts weremade to investigate the liberation of the acyclic phosphineproducts.Bis(viny1) and mixed allylphosphine-vinylphosphine complexesIn an attempt to determine whether intramolecular coupling isintrinsically stubborn in these complexes or other competingreactions render this template approach non-viable, we havestudied similar coupling reactions in a bis(prop-2-enylphos-phine) model complex where the intramolecular coupling canbe limited to one addition between adjacent phosphines.Therequired tetracarbonylbis(prop-2-enylphosphine)chromium(0)complex was readily prepared from [Cr(CO),(MeCN),] andprop-2-enylphosphine (Scheme 2). The product, [Cr(CO),-(H,PC(Me)CH,),] 10, was isolated as a yellow oil fromhydrocarbon solvent and identified by 'P NMR spectroscopy(6 -21.6, 'JpH = 321 Hz). In addition a molecular ion wasobserved in the mass spectrum (m/z 312) and four absorptionsin the IR spectrum due to v(C0) (2066,2017, 1936, 1876 cm-')are consistent with a cis-bis(phosphine)tetracarbonyl arrange-ment of ligands; v(PH) (2305 cm-') and v(C=C) (1623 cm-')were also observed.Heating a solution of 10 in toluene in thepresence of aibn results in rapid reaction to form a newmaterial 11 (Scheme 2), which is identified by an AB pattern inthe ,lP-('H) NMR spectrum (6 5.0, d; 45.6, d; 'JPp = 67 Hz).The former resonance appears as broad triplet in the ,'P NMRspectrum ('JPH = 320 Hz) and hence is assigned to a primaryphosphine; the latter appears as a broad doublet ('.IpH = 317Hz) and is assigned to a secondary phosphine indicating thatcoupling has occurred between adjacent primary phosphinesto give a new diphosphine ligand according to Scheme 2.Clearly, for this di(primary phosphine) complex intramolecularcoupling is facile.An alternative reason for the failure of the templatetriphosphacyclononane synthesis is that the final step to closethe macrocycle may be inhibited by geometric constraintsimposed by the linear triphosphine (i.e. the second intermediate,16 in Scheme 1) required during the course of the reaction.If the constraints of the two carbon backbones between thecoupled phosphorus atoms hold the terminal phosphines toofar apart for the macrocycle to be closed easily, then com-peting intermolecular reactions may predominate resulting inintractable products as was observed. In this case a route totriphosphorus macrocycles with ring sizes intermediate betweentriphospha-cyclododecane and -cyclononane may be possiblewith mixed allylphosphine-vinylphosphine complexes analo-gous to the tris(phosphine) complexes.During the course of thepreparation of 3 an intermediate was observed which wasbelieved to be a partially substituted phosphine-acetonitrileCO10 11Scheme 2 ( i ) Prop-2-enylphosphine, CH,CI,; (ii) aibn, 80 "C1 (iii)12 15Scheme 3 ( i ) Alkenylphosphine (2: l), CH,Cl,; (ii) prop-2-enylphos-phine, CH,CI,; ( i i i ) aibn, 80 OCcomplex (see above). This material was prepared selectively(Scheme 3) by the controlled addition of 2 mole equivalents ofallylphosphine to [Cr(CO),(MeCN),] and was isolated as ayellow oil which was identified as [Cr(CO),(MeCN)(H,P-CH,CHCH,),] 12 spectroscopically.Thus, a singlet was ob-served in the 31P-(1H) NMR spectrum (6 -30.3) and aceto-nitrile was identified in the IR [v(C=N) 2284 cm- '3, 13C-(1H}NMR [6(C-N) 125.41 and 'H NMR spectra [&(Me) 2.121. Inaddition, the molecular ion (m/z 325) was observed in themass spectrum. In a likewise fashion, the bis(viny1phosphine)-monoacetonitrile complexes could be selectively preparedfrom [Cr(CO),(MeCN),] by addition of 2 mole equivalentsof the appropriate primary phosphine and enabling isolationof [Cr(CO) ,( MeCN)( H,PCHCH ,),I 13 and [Cr(CO) , -(MeCN){H,PC(Me)CH,},] 14 as yellow oils and which wereidentified by their NMR spectra [6(3'P) -37.0 and -22.6respectively].Addition of 1 mole equivalent of prop-2-enylphosphine to asolution of complex 12 gave rise to a new triphosphine complexin good yield which was identified as the mixed-phosphinecomplex, [Cr(CO),(H2PCH,CHCH,),(H,PC(Me)CH2}] 15[rather than a mixture of the tris(ally1phosphine) and tris(prop-2-enylphosphine) complexes, 3 and 7, Scheme 31 by 31P-(1H)NMR spectroscopy.Thus two new resonances were observed, atriplet (6 - 1 1.7) and a doublet (6 - 18.2) in an intensity ratio of1 : 2, and conforming to an A,B spin pattern (2Jpp = 29 Hz).Complex 15 appears to be indefinitely stable in solution atambient temperature. However, upon heating in the presence ofaibn proportionation was indicated by the presence of thetriphosphacyclododecane complex 4 as one of the reactionproducts.The other major product from this reaction givesrise to three broad resonances in the 31P-(1H) NMR spectrum(6 45.8, 24.3, -55.2) of approximately equal intensity andwhich can be identified as secondary, secondary and primaryphosphines respectively on the basis of the 'P NMR spectrum[doublet ( 'JpH 324), doublet (324), triplet (335 Hz) respectively].The presence of this product implies that coupling has occurredand on the basis of the ,'P NMR data we propose theformation of a linear triphosphine of the type indicated inScheme 3 where the two allylphosphine groups have coupledleaving the vinyl function pendant. Further heating causesdecomposition and no other products could be characterised. It1804 J. Chem. Soc., Dalton Trans., 1996, Pages 1801-180appears then that the final closing step between the vinylfunction and the remaining terminal primary phosphine isagain relatively slow resulting in unwanted side reactions.Structural studiesIn order to gain insight into the geometrical properties of thetris(a1kenylphosphine) complexes and corresponding influenceson these metal-template coupling reactions, the crystalstructures of the chromium triphosphacyclododecane complex4, and the prop-2-enylphosphine complexes of Cr and Mo (7and 9 respectively) were measured.Selected bond angles andlengths are collected in Table 3 and crystal data in Table 4.The structure of complex 4 (Fig. 1) clearly shows thedistorted fac-octahedral geometry around Cr. The averageCr-P distance [2.326(2) A] is similar to that observed in otherchromium carbonyl phosphine complexes { e.g.2.346(3) 8, infac-[Cr(CO),(PH,),]).S It is slightly shorter than in other trans-[Cr(CO),L(L')] complexes [2.349(4)-2.364(6) A, L = PPh,,L' = PBu,, P(OMe), or P(OPh),] and is 0.13 8, shorter thanthat observed in the molybdenun analogue 5. This relativeshortening of the metal-ligand bonds in the chromium relativeto the molybdenum complex is expected and agrees well with thereported difference in crystal radii.' The average Cr-C distance[1.847(5) 8,] also compares favourably with that in fac-[Cr(CO),(PH,),] [1.838(7) A] and is again 0.138, shorter thanin the molybdenum analogue 5. The interligand bond anglesare close to those for idealised octahedral geometry [averageP-Cr-P angle 91.09(5)"] in 4 and are greater than thoseobserved in 5 [average P-Mo-P 88.88(3)"].The C-Cr-C andcis-P-Cr-C angles are also close to 90" in 4 [average C-Cr-C91.43(2), average cis-P-Cr-C 88.7(1)"] and are similar to thecorresponding angles in 5 [average C-Mo-C 91.7( I), averagecis-P-Mo-C 89.7( l)"]. These minor differences reflect therelative sizes of the metal atoms, thus the size of thismacrocyclic ligand appears to result in a slight expansion of theP-M-P angles around the smaller chromium relative to thosefor molybdenum.The structures of the prop-2-enylphosphine complexes of Cr(7, Fig. 2) and Mo (9, Fig. 3) also show thefac-octahedralgeometry around the metal atoms. Since the interligand anglesare relatively unrestricted in comparison to the macrocyclecomplexes 4 and 5 a more regular octahedral geometry isobserved for both prop-2-enylphosphine complexes [for M =Cr, average P-M-P 89.35(6), cis-P-M-C 90.8( l), C-M-C89.7(2); for M = Mo, average P-M-P 88.47(4), cis-P-M-C91 .O( l ) , C-M-C 89.6(2)"].The average M-P [2.345(2) for 7 and2.501 (1) A for 91 and M-C distances again reflect a reduction incrystal radius (0.16 8,) for Cr in comparison to Mo in thesedirectly analogous complexes. Other structural features are asexpected and the alkene C=C bond [average 1.314(5) for 7 and1.3 15(7) 8, for 91 is readily distinguished from the C-C bond tothe r-methyl group [average 1.510(5) for 7 and 1.503(7) 8, for 91in both complexes. A comparison of the non-bonded P .* * Pdistances in both 7 and 9 with 4 is of interest [average 3.297(4),3.487(5) and 3.321(4) 8, respectively] since it appears that there isonly a slight contraction of the non-bonded P, framework uponcyclisation again indicating that 1,5,9-triphosphacyclododecaneis well suited to match the steric requirements for octahedralco-ordination in these complexes. Clearly comparison withtriphosphacyclononane complexes is not possible as the ligandis still currently unknown, however we have modelled thehypothetical analogue of 4, i. e. (1,4,7-triphosphacyclono-nane)chromium tricarbonyl* in order to estimate the non-bonded P * * * P distances and derive a comparison of therelative sizes of the twelve- and nine-membered macrocycles.* Using CH EM-X molecular simulation software (Chemical Design,Chipping Norton, UK); bond lengths were restricted to the valuesobserved for complex 4 followed by energy minimisation.C(6)Fig.1 Molecular structure and atom-labelling scheme of[Cr(CO), { cycle-( HPC,H,) )] 4Fig. 2 Molecular structure and atom-labelling scheme of fuc-[cr(co)3 (HzPC(Me)CHz)3] 7Fig. 3 Molecular structure and atom-labelling scheme of fac-[Mo(CO),(H2PC(Me)CH2)31 9Simulation generates a P P distance of 2.752 8, and indicatesthat for cyclisation to occur in the vinylphosphine complexes aconsiderable compression of the P-M-P angles is required. Wesuggest that this may be a significant factor in the apparentJ. Chem. SOC., Dalton Trans., 1996, Pages 1801-1807 180Table 3 Selected bond lengths (A) and angles (") for complexes 4,7 and 9M-C( 1 )M-C( 2)M-C(3)M-P( 1 )M-P(2)M-P( 3)O( 1 W(1S0(2kC(2)0(3)-C(3)C(4l-Q 1)C(7)-P(2)C( 12)-P( 1C(6)-P(2)C(9)-P( 3)C(4)-C( 5 )C(4)-C(6)C(7)-C(8)C(7)-C(9)C( 10)-C( 1 1)C( 10)-C( 12)C(5)-C(6)C@)-C(9)C(l1)-C(12)C( 10)-P(3C( 1)-M-C(2)C( 1 )-M-C( 3)C( 2)-M-C(3)C( 1 )-M-P( 1 )C( 1 )-M-P(2)C( 1 )-M-P( 3)C(2)-M-P( 1 )C(2)-M-P(2)C( 2)-M-P( 3)C(3)-M-P( 1)C(3)-M-P(2)C( 3)-M-P( 3)P( 1 )-M-P( 2)P( 1)-M-P(3)P(2)-M-P( 3)O( 1 )-C( I)-MO( 2)-C(2)-MO( 3)-C(3)-MM-P( 1 )-C(4)M-P( 2)-C( 7)M-P( 3)-C( 10)41.829(4)1.869(5)1.844(4)2.342(2)2.3 15(2)2.320(2)1.172(4)1 .146( 5)1.168(4)1.82 l(4)1.845(4)1.826(4)1.847(4)1 .8 3 1 (4)1.839(4)1.525(5)1.5 1 5(5)1.503(5)1.520(5)1.530(5)1.487( 5)90.2(2)91.4(2)92.7(2)178.47( 13)8 8.1 2( 1 4)90.27( 12)90.75( 13)178.20(13)87.88( 13)87.36( 12)88.03(14)178.21( 1)190.92( 4)90.95(5)91.41(5)179.2(3)177.4(4)179.4(4)118.87(14)1 19.76( 14)119.8(2)71.839(4)1.843(4)1.844(4)2.350(2)2.345(2)2.340( 1)1.162(4)1.157(4)1.166(4)1.820(4)1.823(4)1.825(4)1.51 l(5)1.3 I2(5)1.3 18(5)1.5 14(5)1.3 12(5)1.506( 5)89.9(2)90.5(2)88.8(2)178.40( 12)90.58(11)89.81 (1 3)91.82( 12)178.06( 11)9 1.5 1 (12)9 1.05( 12)89.98( 1 1)179.57( 1 1 )89.69(5)88.6 1 (6)89.74( 5)176.4(3)174.5(3)176.8(3)132.83(14)122.68( 13)I 23.2 I ( 14)91.988(5)1.990(5)2.496( 1)2.496( 1)2.51 I ( 1)1,153(6)1.1 46( 5)1.1 36( 5)1.832(5)1.827(5)I .822(5)1.995(5)I .498(5)1.3 15(6)1.508(6)1.310(7)1.321(6)1.504(7)89.7(2)88.0(2)91.0(2)178.33( 13)92.5 1( 13)92.12( 12)9 1.28( 13)176.15( 12)87.20( 12)90.64( 12)92.24( 12)1 78.1 6( 1 2)8 6.5 6( 4)89.26( 4)89.58(4)I76.1(4)178.3(4)176.7(4)1 23 .O( 2)123.8(2)122.1(2)reluctance of our vinylphosphine complexes 7-9 to formtriphosphacyclononane complexes.ExperimentalAll reactions were carried out in an atmosphere of dry nitrogen.All solvents were dried and degassed by boiling under refluxover standard drying agents under a nitrogen atmosphere.Light petroleum had b.p.40-60 "C.The compounds fac-[Cr-(CO),(MeCN),],* ~~C-[MO(CO>,(M~CN),],~ [Mo(CO),-(C,H,Me,-I ,3,5)],9 allylphosphine, ' vinylphosphine and prop-2-enylphosphine '' were prepared by literature methods. Allother chemicals and 'Celite' were obtained from the AldrichChemical Company. The NMR spectra were recorded on aBruker WM360 instrument operating at 360.13 ('H) and 90.53(13C) MHz or a JEOL FX-90 instrument operating at 36.23(, 'P) MHz. All NMR spectra were recorded in CDC1, solution,with the 'H and I3C chemical shifts quoted in ppm relative tosolvent and 31P chemical shifts quoted in ppm relative to 85%external H3PO4 (6 0); + 6 values refer to chemical shifts down-field from the standards. The IR spectra were recorded inNujol on a Nicolet 510 FT-IR spectrometer.Mass spectra andmicroanalyses were obtained from within this department.CAUTION: The organophosphines and some of theircomplexes described are highly malodorous and likely highlytoxic. Care should be exercised in their handling.PreparationsTris(primary phosphine) metal tricarbonyl complexes. Thesyntheses of complexes 3,7,8 and 9 were very similar and so ageneral method is described. To a frozen solution of phosphine[ 13.5 mmol, allylphosphine (3), prop-2-enylphosphine (7 and9), vinylphosphine (S)] in toluene (50 cm3) was added fac-[M(CO),(MeCN),] (3.3 mmol, M = Cr 3, 7, 8 or Mo 9). Themixture was allowed to warm to room temperature and stirredfor 8 h. Following removal of solvent and unreacted phosphinein uacuo, the product remained as a yellow oil in almostquantitative yields.Purification was by recrystallisation fromlight petroleum.[Cr(CO),{cyclo-(HPC,H,),}] 4. To a solution of complex 3(1.07 g, 3.0 mol) in toluene (250 cm3) was added a catalytic (ca.1% w/w) amount of aibn and the mixture heated to 80-100 "Cfor 4 h. The mixture was allowed to cool to room temperatureand filtered through a short (4 cm) Celite column to give a yellowsolution. The solvent was removed in uucuo to give a viscousyellow oil which was recrystallised from toluene at - 20 "C togive the product as colourless crystals (yield = 0.87 g, 8 1%).cis-[ Cr(CO),{H,PC(Me)CH,},] 10. This complex wasprepared ( > 90% yield) in an identical manner to 7, using cis-[Cr(CO),(MeCN),] as the starting material and giving an oilupon evaporation of the reaction solution in uucuo.The residuewas dissolved in CH,Cl, and passed down a short (2.5 cm)Celite column. The solvent was removed in uucuo to give thecrude product as a yellow oil which was further purified byrecrystallisation from light petroleum.[ Cr(CO),(H,PCH(Me)CH,P(H)C(Me)CH,)] 11. This com-plex was prepared (85% yield) by an identical method to that for4, using 10 as the starting material.[ Cr(CO),(MeCN)(H,PCH,CHCH3,] 12. To a frozensolution of allylphosphine (10.0 mmol) in toluene (50 cm3) wasadded fac-[Cr(CO),(MeCN),] (5 mmol). The mixture wasallowed to warm to room temperature and stirred for 4 h.Removal of solvent in uacuo generated the product as a yellowoil in almost quantitative yields.Purification was byrecrystallisation from light petroleum.[ Cr(CO),(H,PCH,CHCH,),(H,PC(Me)CH,)] 15. To afrozen solution of prop-2-enylphosphine (5.0 mmol) in toluene(50 cm3) was added a solution of complex 12 (1.63 g, 5 mmol) intoluene (50 cm3). The mixture was allowed to warm to roomtemperature and stirred for 8 h. The solvent was removed inuaeuo to give the product as a yellow oil in almost quantitativeyield. Purification was by recrystallisation from toluene-lightpetroleum.CrystallographyData collection and processing. ' ' Data were collected on aDelft Instruments FAST TV area detector diffractometer,X-rays being produced by a rotating-anode generator usinga molybdenum target [h(Mo-Ka) = 0.71069 A], and beingcontrolled by a Micro Vax 3200 computer, driven byMADNES l 2 software.All data sets were recorded at 120 Kusing an Oxford Cryostream low-temperature cooling system.Data reduction was performed using the ABSMAD 'program.Structure determination and refinement. The structures weresolved by heavy-atom methods (SHELXS 86 14) and subjected1806 J. Chem. SOC., Dalton Trans., 1996, Pages 1801-180Table 4 Crystal data for compounds 4, 7 and 94Empirical formula C12H21Cr03P3M , 358.2Crystal system MonoclinicSpace group p2 1 lc 4hlAciA@I"Pi" 92.96(4)Yi"UjA 3 1586.6( 14)Z 4Dclgcm 1.500F(OO0) 744Pimm ' 1.023Crystal size/mmNo. reflections collected 64331 2.52 1 (7)8.458(4)15.002(7)0.25 x 0.145 x 0.070 Rangel" 2.72-24.94hkl Ranges - 14 to 12, -9 to 9, - 17 to 14No.unique data 234 1R,", 0.051 7wR2" (all data) 0.0814R, (all data) 0.06 19No. parameters I84wR, (F, > 40F0)R , (F, > 40F0) 0.0352Pln,,? Pmlnle A 0.45, -0.2710.074 (1 571 data)" wR, = [Cw(FO2 - Fc2)2/C~(Fo2)2]'. R1 = C(Fo - Fc)/Z(FJ.7358.2Monoclinic6.65 l(4)15.292(7)17.308(6)C12H21Cr03P3p2 1 In93.92(7)1756(2)41.3557440.9240.29 x 0.1 1 x 0.03545081.78-24.91- 5 tO5, -13 to 16, -22840.03 170.07860.04891990.0766 (1 7 15 data)0.03320.456, -0.2989402.14TriclinicPT6.7058( 5)11.5523(12)12.4224(9)74.968( 13)75.6( 2)78.804(7)891.53( 13)21.4984081.0050.2 x 0.14 x 0.143824C12H21M003P32.8-24.98-7 to 5, - 12 to 13, - 18 to 1325030.04820.09220.041 81990.0902 (2193 data)0.03671.1 17, -0.53114 to 14to full-matrix least-squares refinement based on Fo2 (SHELXL93 l').Non-hydrogen atoms were refined anisotropically withall hydrogens included in idealised positions, having isotropicthermal parameters riding on the value of their parent atoms.An absorption correction (DIFABS 16) was applied to all threestructures. The weighting scheme used was w = 1/[o2(FO2)].Diagrams were drawn with SNOOPI. '' Sources of scatteringfactor data were from the literature.I6Atomic coordinates, thermal parameters and bond lengthsand angles have been deposited at the Cambridge Crystallo-graphic Data Centre (CCDC). See Instructions for Authors,J. Chem. SOC., Dalton Trans., 1996, Issue 1.Any request forthis material should quote the full literature citation and thereference number 186/17.AcknowledgementsWe thank the EPSRC for a research grant (to J. S. F.) andsupport for X-ray facilities. We would also like to thank TheAssociation of Commonwealth Universities and University ofSri Jayewardenepura of Sri Lanka for a scholarship (to S. S. L.).References1 B. N. Diel, P. F. Brandt, R. C. Haltiwanger and A. D. Norman,J . Am. Chem. Soc., 1982, 104, 4700; B. N. Diel, P. F. Brandt,R. C. Haltiwanger, M. L. J. Hackney and A. D. Norman, Inorg.Chem., 1989,28,28 1 1 and refs. therein.2 S. J. Coles, P. G. Edwards, J. S. Fleming and M. B. Hursthouse,J. Chem. Soc., Dulton Trans., 1995, 1139.3 K. 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Messerschmidt, MADNES, version 1 113 ABSMAD, Program for FAST data processing, A. I. Karaulov,14 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990,46,467.15 G. M. Sheldrick, University of Gottingen, 1993.16 N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39,158; adapted for FAST geometry by A. I. Karaulov, University ofWales, Cardiff, 1991.Inorg. Chem., 1993,32,4653.September 1989, Delft Instruments, Delft, 1989.University of Wales, Cardiff, 1992.17 K. Davies and K. C. Prout, University of Oxford, 1993.Received 25th October 1995; Paper 5/07032EJ. Chem. Soc., Dalton Trans., 1996, Pages 1801-1807 180