J. CHEM. SOC. DALTON TRANS. 1994 1Synthesis and Photochemical Reactivity ofPhenylthioureatotriosmium Cluster Complexes: CrystalStructures of [Os,H (CO),,{p-SC( NPh)( NH Ph)}] and[OS~H(CO),{~~-SC(NP~)(NHP~)}] *Eric W. Ainscough/ Andrew M. Brodie,a Scott L. Ingham,a Thomas G. Ketch?Alistair J. Lees,c Jack Lewisd and Joyce M. Watersaa Department of Chemistry and Biochemistry, Masse y University, Palmerston North, New ZealandDepartment of Chemistry, State University of New York at Binghamton, P.O. Box 6000, Binghamton,Department of Chemistry, University of Central Lancashire, Preston PRI 2HE, UKUniversity Chemical Laboratory, Lensfield Road, Cambridge CB2 I EW, UKN Y 13902 - 6000, USAThe reaction of [0s3(C0),,( MeCN),] with phenylthiourea (H L') and N,N'-diphenylthiourea ( H L2) yieldedthe thioureatotriosmium cluster complexes [Os,H(CO),,(p-L)] ( L = L' or L2) in which the thioureatemoiety L bridges two osmium atoms via the sulfur atom.The complexes underwent photochemicalreactions with a nitrogen atom of the thioureate ligand displacing a carbonyl on the third osmium atom togive [Os,H(CO),(p,-L)] (L = L1 or L2). These reactions proceed cleanly and the quantum yields andapparent activation energies have been determined. The cluster complexes have been characterized byspectroscopic means and the structures of [Os,H (CO),,(p.-L2)] and [Os,H (C0),(~,-L2)] have beendetermined by X-ray diffraction: [ O S , H ( C O ) ~ ~ ( ~ - L ~ ) ] , triclinic, space group PI, a = 11.607(3),b = 14.341 (3), c = 9.520(3) p\, x = 104.92(2), p = 11 2.62(2), y = 94.02(2)", and Z = 2, [Os,H(CO),-(p3-LZ)], monoclinic, space group P2,/m, a = 9.583(3), b = 14.249(3), c = 9.969(3) A, p = 103.53(2)",and Z = 2.The structures were refined to R = 0.035 and 0.046 for 3791 and 3987 unique diffraction datarespectively. In both clusters one edge of the osmium triangle is bridged by a sulfur atom and in[Os,H(CO),(p,-L2)] one of the nitrogen atoms of the thioureate ligand has displaced a carbonyl from thethird osmium of the cluster.Phenylthiourea and N,N'-diphenylthiourea form complexeswith a number of transition metals and their study has attractedconsiderable attention over the past twenty years.'-' For theneutral ligands co-ordination is normally via the sulfur atomacting as a monodentate although a few examples ofdeprotonated phenylthiourea complexes have now beenstructurally characterized and in all cases the ligand, as withother thioureato-ligands, chelates via both the sulfur andnitrogen donor atom^.^.^ l4 It appears that in no case has adeprotonated thiourea been characterized in which only thesulfur atom is co-ordinated, but the high affinity of triosmiumclusters for thiolate and hydride ligands has allowed this modeof co-ordination to be achieved in the complexes [Os,H-(CO) o( p-L)] (HL = phenylthiourea or N,N'-diphenylthio-urea).These complexes are highly photochemically active,readily decarbonylating in visible light to yield [Os,H(CO),-(p3-L)] cluster complexes (Scheme 1). A detailed study ofthis photochemical conversion has therefore been made todetermine quan tum yields and activation energies.Results and DiscussionThe ligands phenylthiourea (HL') and diphenylthiourea (HL2)react smoothly in refluxing dichloromethane with 1 equivalentof [Os,(CO),,(MeCN),] to yield, after purification by TLC, thep-hydrido-p-thioureato-decacarbonyltriosmium clusters [Os,-H(CO),,(p-L')] and [0s,H(CO),,(p-L2)] as yellow crystalline* Supplementury ciuta available: see Instructions for Authors, J.Chem.Soc., Dalton Trans., 1994, Issue 1, pp. xxiii-xxviii.Scheme 1NMR assignments in Table 1. R = H (L') or Ph (L')Photoconversion and ligand atom-numbering scheme formaterials. These compounds are stable at room temperature inair, and for a moderate time (24 h) in the dark in solution.Decarbonylation can be achieved by either photolysis of acyclohexane solution or by reaction in dichloromethane withtrimethylamine N-oxide to produce [Os3H(CO),(p3-L)](L = L' or L').The photolysis proceeds readily withquantitative conversion into the corresponding nonacarbonyl-triosmium compounds and hence this is the method of choicefor preparing these clusters. All compounds were characterizedby spectroscopic means and elemental analyses. Hydrogen- 1and carbon- 13 NMR spectral data are given in Tables 1 and 2.Assignments have been made by comparison with the parentthioureas 5 9 1 6 and related triosmium thioamido complexes.The expected NH and OsH resonances are observed and for theL2 complexes the ' NMR spectra exhibit separate resonance2 J.CHEM. SOC. DALTON TRANS. 1994Table 1 Proton and I3C NMR data"'H(6)b ' 3C(S) =Compound NH OsH C' C2 c3 c4 C51% H(CO) I o (P-L 11 4.99 (2 H) - 17.31 (1 H) 157.3 146.7 121.1 129.7 123.9[OS3H(CO)i o(P-L2)1 6.49 (1 H) - 17.46 (1 H) 156.2 146.1 121.1 129.8 123.9(137.9) (125.9) (129.0) (126.7)[os3 H(CO) 9(P 3-L 11 5.1 br (2 H) - 11.83 (0.14 H) 182.1 148.8 121.9 130.7 127.7H(CO) 9 (P3-L2)1 6.32 (1 H) -11.60(0.14H) 183.1 149.9 122.2 131.1 127.9- 14.94 (0.86 H)- 14.90 (0.86 H) (137.4) (126.3) (129.5) (128.1)a In CDCI3 at 25 "C. For atom numbering see Scheme 1. CH resonances not listed. For L2 complexes the resonances for the second phenyl ring aregiven in parentheses. 3C NMR data at - 50 OC. Assignments may be interchanged.Table 2 Carbonyl 3C NMR data (6) *D F E 4CompoundCOs3H(CO)i o(P-L')I 181.3, 180.0 173.9 176.7, 170.4 169.3[0s3H(C0)1 0(P-L2)1 180.7, 180.0 173.9 176.5, 170.9 168.8C PA R E[OS3H(C0)9(P3-L1)l 187.2 181.5 179.5, 176.0 175.7~ ~ ~ ~ ~ ( ~ o ) ~ ( P 3 - ~ 2 ) ~ 187.4 181.6 179.5, 176.4 175.5* In CDCl, at 25 "C.Relative intensities: for [Os3H(CO),,(~-L)], 1 forA and B, 2 for C-F; for symmetrical form of [Os,H(CO),(p3-L)], 1 forB, 2 for A and C-E.for each of the phenyl rings. For the [Os,H(CO),,(p-L)]complexes six carbonyl resonances with a relative intensitypattern of 1 : 1 : 2 : 2 : 2 : 2 as expected for the symmetricalstructure determined by X-ray analysis (see below) are seen. Foreach of the two nonacarbonyl complexes, [OS,H(CO)~(~,-L)],two osmium hydride signals are observed with relativeintensities 0.86 : 0.14, pointing to the presence of two isomers.Carbon-13 NMR spectra show the major isomer is thesymmetrical one in which the hydride ligand bridges the sameedge of the osmium triangle as does the thioureate sulfur atomsince five signals are seen for the carbonyl carbons with relativeintensity 1 : 2 : 2 : 2 : 2.For the unsymmetrical case where thehydride bridges the non-equivalent osmiums, each CO group isunique and nine resonances should be observed although nonewas detected above the background noise.Single-crystal Structures of [Os,H(CO), ,(p-L2)] and[Os,H(CO),(p,-L2)].-Thermal ellipsoid diagrams of the twocompounds including the numbering system are shown in Figs.1 and 2.Fractional atomic coordinates are listed in Tables 3 and4, selected bond lengths and angles in Tables 5 and 6. In bothspecies the osmium atoms define a triangle with the sulfur atomof the thioureate moiety bridging one edge of the triangle; thisedge is also bridged by a hydride ligand.In [Os,H(CO), ,(p-L2>] the 0s-0s distances observed[2.853( l), 2.866( I), 2.869( 1) 8,] are slightly shorter than theaverage metal-metal distance of 2.877(3) 8, found in [Os,-Fig. 1 Molecular structure of [Os3H(CO),,(~-L2)]. Thermalellipsoids are drawn at the 50% probability level; N(l) is the amido Nand N(01) is the imino NFig. 2 Molecular structure of [Os3H(CO),(p3-L2)]. Details as in Fig. 1(CO),2],18 but lie well within the range observed for other p-H,p-S decacarbonyltriosmium clusters 7*19-22 of 2.837-2.876 A.The sulfur atom of the diphenylthioureate ligand bridgesbetween Os(2) and Os(3) with bond lengths of 2.395(2) and2.409(2) 8, respectively, these distances being consistent withthose found in other p-S triosmium 2 2 Within theligand the thioureate moiety is planar with the carbon-sulfurbond distance at 1.813(9) 8, in the range for a single bonJ.CHEM. SOC. DALTON TRANS. 1994 3Table 3 Fractional atomic coordinates for [Os,H(CO), ,(p-L2)] with estimated standard deviations (e.s.d.s) in parentheses0.185 08(3)0.240 08(3)0.440 72(3)0.097 6(8)0.282 9(10)0.008 l(8)0.41 5 O(8)0.312 l(10)0.490 2(8)0.685 l(10)0.548 9( 12)0.006 9( 10)0.193 9(10)0.245 4(10)0.088 9(10)0.349 5(10)0.288 O( 12)0.202 O(2)0.1896(10) -0.386 3(8) -0.143 36(3)0.192 95(3)0.170 67(3)0.303 O(2)0.1 18 2(7)0.069 2(6)0.219 l(8)0.181 6(7)0.361 7(6)0.035 7(7)0.393 O(5)0.047 4(5)0.218 6(8)0.1 12 5(6)0.128 5(7)0.013 O(8)0.190 5(8)0.189 9(8)0.295 O(9)0.094 O(9)0.244 80(4)0.001 23(4)0.276 32(4)0.208 3(3)0.175 O(12)0.239 3( 14)0.605 6( 10)0.000 6( 12)0.448 7(10)0.079 O( 1 1)0.233 3( 15)0.580 9( 10)0.196 l(14)0.243 7(13)0.472 2( 13)-0.303 l(9)-0.216 8(11)-0.184 5(12)- 0.005 5( 12)-0.132 2(13)0.464 3(10)0.401 9(9)0.592 4(12)0.51 1 4(11)- 0.01 8 5(7)0.008 9(9)0.043 3(9)0.080 O( 10)0.192 6(12)0.262 5( 15)0.212 4(14)0.099 7( 18)0.031 7(13)-0.142 5(9)- 0.167 O(9)-0.288 8(11)-0.388 5(11)- 0.364 8( 10)- 0.243 8(9)0.1210.311 O(7)0.033 9(7)0.198 3(9)0.136 O(7)0.3 15 2(6)0.372 6(7)0.330 4(6)0.403 7(7)0.469 4(8)0.502 2( 10)0.469 9(9)0.403 3( 10)0.368 l(8)0.339 O(7)0.413 6(7)0.434 2(9)0.379 3(9)0.301 4(8)0.280 3(7)0.104Z I C0.385 8( 12)0.149 7(12)0.244 6( 14)0.470 5( 12)0.254 2( 10)0.1 34 4( 1 1)0.422 5(11)0.494 4(14)0.661 l(16)0.749 8( 15)0.682 9( 17)0.515 3(14)- 0.012 3(9)-0.0664(10)-0.131 8(11)-0.187 8(13)-0.182 l(13)-0.120 8(13)- 0.058 2( 12)0.020Table 4e.s.d.s in parenthesesFractional atomic coordinates for [OS~H(CO)~(~,-L')] withXla0.219 52(2)0.257 85(3)0.468 3(3)0.019 2(12)0.100 6(8)0.202 8(9)0.185 l(10)0.347 4(9)0.289 2(8)0.307 O(10)0.074 9( 10)0.033 2(7)0.681 2(10)0.449 3(9)0.538 3(9)0.780 O( 10)0.827 9(10)0.93 1 2( 13)0.984 8(20)0.513 2(11)0.541 l(12)0.598 7( 14)0.635 l(18)0.1 160.401 2(9) -YJh0.250 00.149 80(2)0.250 00.250 00.250 00.354 2(6)0.41 7 8(7)0.054 9(7)0.099 6(6)0.067 3(7)0.092 7(6)0.059 2(6)0.250 00.250 00.250 00.250 00.334 l(7)0.333 3(8)0.250 00.250 00.332 l(11)0.250 0 -0.250- 0.000 9(6)0.331 8(15) -ZIC0.214 56(4)0.460 93(3)0.520 3(3)0.201 7(12)0.196 l(13)0.089 8( 10)0.01 8 6(9)0.379 4( 11)0.325 3( 10)0.646 7(9)0.757 4(9)0.398 l(10)0.358 8( 10)0.391 5(8)0.250 2( 8)0.370 9( 11)0.524 7( 10)0.586 6( 10)0.712 O( 11)0.775 2( 16)0.131 4(11)0.072 8( 13)- 0.044 6( 13)- 0.097 O( 15)0.479(1.80-1.82 ~ 4 ) .~ ~ - ~ ~ The carbon-nitrogen lengths C-N(1) andC-N(O 1 ) at 1.36( 1) and 1.25( 1) 8, indicate appreciable double-bond character for the latter.26 Each of the phenyl rings,C( 1)-C(6) and C(Ol)-C(06), is planar and they lie at angles of58.3 and 7 1.1 O respectively to the plane of the thiourea moietycontaining atoms S, C, N( 1) and N(O1). They form an angle of62.2" with respect to one another. The bridging hydride ion waslocated on a difference electron-density map; it forms a bridgebetween Os(2) and Os(3) at distances of 1.91 and 1.88 8, and lieson the opposite side of the Os(2)-Os(3) edge to the sulfur atom.The hydride lies 0.88 8, above the plane of the osmium trianglewith the sulfur 1.89 8, below.The amido proton H(N1) was alsoclearly visible on a difference-electron map bonded to N( 1) at adistance of 0.98 A.The complex [OS~H(CO)&~-L~)] differs from [Os3H-(CO)lo(p-L2)] in the additional co-ordination of one of thenitrogen atoms of the thioureate ligand to the third osmium ofthe triangle. The sulfur of the ligand and the hydrido atomTable 5(p-L')] with e.s.d.s in parenthesesOs( 1)-Os(2) 2.869(1) s-c 1 .8 1 3(9)OS( 1 t o s ( 3 ) 2.853( 1) C-N( 1 ) 1.362( 12)Os(2)-Os(3) 2.866(1) C-N(0 1 ) 1 .25 1 ( 1 2)1.419( 13) OS(2FS 2.395(2)Os(3)-S 2.409( 2) "1 )-H(N 1) 0.98Os(2)-H 1.91 N(O1 )-C(0 1) 1.428( 1 1)OS( 3)-H 1.88Os( l)-Os(2)-Os(3) 59.7( 1) 0~(3)-0~(2)-H 40.5Os( l)-Os(3)-Os(2) 60.2(1) Os( 2)-s-c 1 12.0(3)OS( 2)-0~( 1 )-OS( 3) 60.1 ( 1 ) Os( 3)-s-c 107.7(3)OS(2)-S-OS(3) 73.2( 1) S-C-N( 1 ) 11 2.7(7)OS(2)-OS(3)-S 53.2(1) S-C-N(O 1 ) 119.9(7)OS( 2)-H-0~( 3) 98.2 C-N( 1 K( 1 ) 130.3(8)Selected bond lengths (A) and angles (") for [Os,H(CO),,-NU k C ( 1)Os( 3)-0s( 2)-s 53.6( 1) N( 1 )-C-N(O 1 ) 127.3(9)Os( 2)-0s( 3)-H 41.3 C-N(OlkC(01) 118.5(8)Table 6(CO),(p,-L')] with e.s.d.s in parenthesesSelected bond lengths (A) and angles (") for [Os,H-OS( 1 )-Os( 2) 2.790( 1 ) C-N( 1 ) 1.336( 12)OS(2)-0S(2') 2.856( 1) C-N(O 1 ) 1.302( 13)Os(2)-H 2.0 1 N(Ol)-C(Ol) 1.455(12)s-c 1.770(11)OS(2)-S 2.428( 2) N ( l K ( 1 ) 1.439( 13)Os(2)-Os(l)-Os(2') 61.6(1) C-N(OlkC(O1) 116.4(8)Os( 1 )-Os(2)-0s(2') 59.2( 1) N(1)-C-N(O1) 124.6(9)Os(2)-S-Os(2') 72.1 (1) S-C-N( 1 ) 116.6(7)0~(2)-H-0~(2') 90.4 S-C-N(O1) 118.8(7)Os(2)-S-C 104.6(3) C-N(IkC(1) 124.8(8)bridge the same edge of the triangle as was found in thedodecacarbonyl analogue.The molecule lies on a crystallo-graphic mirror plane and hence possesses C, symmetry. TheOs(2)-Os(2') bond distance at 2.856(1) 8, is as expected,however, the Os(l)-Os(2) length at 2.790(1) 8, is significantlyshorter than comparable distances in other comparabletriosmium species as well as in [Os,H(CO),,(p-L2)]. Sincesteric factors are known to be important in controlling thelength of bridged Os-0s bonds 2 7 the shortening of the Os-0sdistance can be explained in terms of the geometricalrequirements of the p3 ligand as it caps the osmium triangle.Inline with this there is a concomitant lengthening of the averageOs-S distance of 0.026 A when the diphenylthioureate ligand isconverted from a doubly into a triply bridging mode. A simila4 J. CHEM. SOC. DALTON TRANS. 1994shortening of Os-Os and lengthening of 0s-S bonds has beenobserved for the thioformamido complexes, [OsH(CO), o(p-L)]and [OsH(CO),(p3-L)] [L = SC(H)=NC6H,F-p].'0For [OS~H(CO)~(~,-L~)] the carbon-sulfur distance of1.77(1) 8, is also consistent with that of a C-S single bond 23-25and does not differ significantly from the value observed in[0s3H(C0),,(p-L')]. At 1.34(1) 8, the carbon-nitrogen bondlength, C-N(l), is in agreement with that found in[Os3H(CO),,(p-L2)] and is similar to that expected for asingle bond.'' However, the imino carbon-nitrogen bondlength, C-N(Ol), at 1.30(1) A, is longer than that observed in[Os,H(CO),,(p-L2)] by 0.05 A. The phenyl rings C(l)-C(4)and C(O1 )-C(04) lie astride the crystallographically imposedmirror plane and are orthogonal to the plane containingthe thioureate moiety. They lie at an angle of 113.4' to oneanother.The bond distances and angles associated with the carbonylligands in both complexes are as expected with ranges of1.878(10)-1.958(10) and 1.884(9)-1.942(8) 8, for the 0s-Cdistances in [Os3H(CO),,(p-L2)] and [ O S ~ H ( C O ) ~ ( ~ ~ - L ~ ) ]respectively. Corresponding ranges for C-0 and 0s-C-0 are1.12(1)-1.16(1) 8, and 172(1)-179(1)', and 1.13(11)-1.17(1) Aand 175.5(9)-178.9(9)' respectively for the two clusters.Thesevalues are in agreement with similar data observed in otherosmium carbonyl clusters. 9,3Photolysis of [Os,H(CO),,(p-L)] (L = L' or L2).-Thephotochemical conversion of [Os,H(CO),,(p-L)] into [Os,H-(C0),(p3-L)] (L = L' or L2) was monitored by both IR andUV/VIS spectrcscopy (Fig. 3). The decrease in intensity of thev(C0) IR band at ca. 21 10 cm-' and the growth of the band atca. 2085 cm-' are convenient indicators for the photoconversion.The reactions proceed cleanly without interference fromsecondary processes or thermal decomposition as indicated bythe sharp isosbestic point observed for each compound in itsUVjVIS spectrum. The most significant features in the spectraare the decrease at 330 nm and increase at 375 nm observed asthe reaction proceeds.Quantum yields, <D, at 293 K have beendetermined at an irradiating wavelength of 366 nm in cyclo-hexane with an incident light intensity of 1.95 x 10 -5 mol dm-3s-' (determined by ferrioxalate actinometry). Values of 0.064(average of three measurements) and 0.054 (average of fourmeasurements) were observed for compounds [OsH(CO),,-(p-L')] and [Os3H(CO),,(p-L2)] respectively showing thatboth photoconversions proceed with relatively high efficiency.The values are considerably greater than those reported for thephotolytic mercury-extrusion from [os, 8Hg3C2(C0)42]2 - and[Os, ,Hg,C,(CO),,] - (ca. lop3) 3 1 possibly due to the largernumber of non-radiative decay and bond-cleavage routesavailable in these latter clusters resulting from their increasedsize.The results obtained for the apparent activation energies of4.7 kJ mol ' for [Os,H(CO),,(p-L')] and 3.9 kJ mol-' for[Os3H(CO),,(p-L2)] (Table 7) are very low, possibly reflectingsolvent-displacement processes in the photoreaction as thecarbonyl ligands are ejected from the parent complexes. Therelatively high photoefficiency and extremely low apparentactivation energy of these photoconversions strongly suggestthat the initial step of carbonyl dissociation for thesephotoreactions occurs from a ligand field-type excited state.These ligand-field or d-d type excited states often undergo facileligand dissociation with low activation energy barriers.32,33Ligand labilization by ligand-field excited states can beexplained if the highest-occupied metal d orbitals are bondingwith respect to the M-CO linkage and the lowest-unoccupiedset of metal d orbitals is strongly antibonding with respect to theM-CO bond. Thus it may be considered that the lowestphotoexcited states are those for transitions at the metal centrewhich result in electron density going from bonding toantibonding orbitals, weakening one or more M-CO bonds andleading to carbonyl dissociation. The conversion of [Os,H-(CO),,(p-L)] into [Os3H(C0),(p3-L)] also results in a shift toTable 7 Photochemical quantum efficiencies for the 366 nm irradi-ation of [Os3H(CO),,(~-L')] and [Os3H(CO),,(p-L2)] complexes indeoxygenated cyclohexane at various temperaturesQ, E,*/kJ mol-'0.054 4.70.0580.0640.0650.048 3.90.0500.0540.05610.1 61300 340 380 420 460 500AJnm21'21 ' 2077 ' 2033 ' 1989 1945Wave nu m be r/cm-'Fig.3 (a) The UVjVIS changes accompanying the photolysis at 366nm of 6.2 x mol dmW3 [Os,H(CO),,(~-L')] in deoxygenatedhexane at 293 K. Spectra were recorded at 30 s photolysis intervals;initial spectrum recorded prior to photolysis. ( b ) The IR spectralchanges accompanying the photolysis at 366 nm of cu. 7 x moldm-3 [Os,H(CO), ,(p-L1)] in deoxygenated methylcyclohexane at293 K. Other details as in (a)lower energy of the d-d band, which is consistent with theincreased substitution at the triosmium frame. A lowering of theenergy for the d 4 transition has also been reported forincreasing substitution of tertiary phosphines on triosmiumclusters,34 and can be attributed to the replacement of thestrongly n-accepting carbonyl ligands, resulting in a decrease inthe average ligand-field splitting, which in turn results in alowering of the energy of the d 4 transition.ExperimentalInfrared spectra were recorded on cyclohexane solutions in 0.5mm NaCl cells on a Bio-Rad FTS-40 spectrophotometer, masJ. CHEM.SOC. DALTON TRANS. 1994 5spectra using a Varian VG70-250s instrument using theliquid secondary ion mass spectroscopy (LSIMS) methodfrom samples in a m-nitrobenzyl alcohol matrix andhydrogen-1 and carbon-13 NMR spectra using a JEOLGX270W instrument.Solvents were purified and dried in the usual manner andreactions performed under dinitrogen.The starting complex[Os,(CO) ,(MeCN),] was prepared by the reaction of[Os,(CO) ,] with trimethylamine N-oxide according to aliterature method., Phenylthiourea (HL') was prepared fromaniline according to Frank and Smith36 and N,N'-diphenyl-thiourea (HL') was obtained from Aldrich. Product purifi-cation was achieved using thin-layer chromatography (TLC)with plates coated with Fluka GF254 silica gel to a thicknessof 1 mm. Microanalyses were performed by the CampbellMicroanalytical Laboratory, University of Otago.Syntheses.-[O~,H(CO)~,(p-L')]. To a CH,Cl, solution (1 5cm3) of [Os,(CO),,(MeCN),] (46.6 mg, 0.05 mmol) was addedphenylthiourea (7.6 mg, 0.05 mmol) dissolved in the samesolvent ( 5 cm3). The solution was stirred at room temperaturefor 15 min, refluxed for 5 min and then allowed to cool.Thesolvent was removed under vacuum and the yellow crystallineproduct purified by TLC [CH,Cl,-hexane (1 : 1) as eluent].Yield: 38.3mg, (76%)(Found: C,20.10; H,0.75;N, 2.80. Calc. forC, 7H,N20100s3S: C, 20.35; H, 0.80; N, 2.80%). Mass spectrum:m/z = 1008 [M+ ('920s)]. IR[v(CO)]: 2108m, 2070vs, 2060s,2022vs, 201 3s, 2004s, 1995m and 1983ms cm-'.[0s3H(C0),,(p-L2)]. This complex was prepared in amanner similar to that described above using N,N'-diphenyl-thiourea (1 1.4 mg, 0.05 mmol). Yellow crystals of the productwere obtained after TLC [CH,Cl,-hexane (1 : 4) as eluent].Yield 44.2 mg (82%) (Found: C, 25.45; H, 1.00; N, 2.75.Calc.for C,,H,,N,O,,Os,S: C, 25.60; H, 1.10; N, 2.60%). Massspectrum: m/z = 1084 [M' ('920s)]. IR[v(CO)]: 2109m,2070vs, 2060s, 2023vs, 2014s, 2004s, 1989m and 1985m cm-'.[0s3H(C0),(p3-L1)]. A cyclohexane solution of thedodecacarbonyl complex [Os,H(CO), ,(p-L')] can be quan-titatively converted into [Os3H(C0),(p3-L1)] by irradiation ofa solution with visible light. Typically, samples were dissolved incyclohexane in a water-cooled cell and irradiated until thereaction was complete as determined by IR spectroscopy in thev(C0) region. Yellow-orange crystals were obtained fromCH,Cl,-hexane (Found: C, 19.90; H, 0.80; N, 2.95. Calc. forC16H8N2090~3S: C, 19.70; H, 0.85; N, 2.85%). Mass spectrum:m/z = 980 [M' ('920s)]. IR[v(CO)]: 2085m, 2053vs, 2030vs,2001s, 1985s, 1964m and 1955m cm-'.The complex was also less conveniently prepared by heatingtrimethylamine N-oxide and the parent dodecacarbonylcomplex in CH,Cl, followed by purification using TLC[CH,Cl,-hexane eluent (1 : l)].[Os,H(CO)&,-L)]. This complex was prepared in a manneridentical to that described for the p3-L1 complex (Found: C,25.35; H, 1.20; N, 2.50.Calc. for C,,H,,N,O,Os,S: 25.15;H, I . 15; N, 2.65%). Mass spectrum: m/z = 1056 [M+ ("*Os)].IR[v(CO)]: 2084m, 2052vs, 2030vs, 2000s, 1984s, 1963m and1954m cm-' .Single-crystal Structural Determinations of [Os,H(CO),,-(p-L2)] and [Os,H(CO),(p,-L2)].-Crystal data and datapertaining to data collection and structure refinement are givenin Table 8 for both compounds.Crystals suitable for diffractionstudies were grown from a hexane-CH,Cl, mixture andmounted on glass fibres on a Enraf-Nonius CAD4 diffractometerequipped with graphite-monochromated Mo-Ka radiation.Intensity data were collected at 293 K in the w28 mode toOm,, = 25" ( + h , k k , k 1) for [OS,H(CO)~,(~-L~)], and 8 =35" (+ h, + k , k 1) for [Os3H(C0),(p3-L2)] and corrected forLorentz and polarization effects. Crystal stability wasmonitored hourly by the observation of the intensities of threestandard reflections. Crystal decay was linear { 3.4% forTable 8(co)9(P3-L2)1Crystallographic data for [OS~H(CO),~(~-L~)] and [Os3H-[o S 3H(CO) 1 o(P-L2 11 COS, H(CO) 9 (P3-Lz)IFormula C23H12N20100s3S C22H12N2090s3SM 1079.02 1051.01Crystal size/mmCrystal system Triclinic Monoclinic0.31 x 0.10 x 0.16 0.34 x 0.44 x 0.12Space group PT p2 1 lmalAblA 4xioPI"rl" u p 1387.9 z 2 2DJg cm-3 2.582 2.637F(OO0) 976 94811.607(3) 9.5 83( 3)14.341(3) 14.249( 3)9.520( 3) 9.969( 3)104.92(2)112.62(2) 1 03.5 3( 2)94.02(2)1323.4p(Mo-Ka)/cm-' 138.5 145.1ernaxlo 25 35Unique data 4561 5734Indices explored +h, fk, f I +h, + k , + IMerging R 0.019 0.037(based on I)Data with 3791 3987F, 2 3W0)Parameters refined 354 185R" 0.035 0.046R' a 0.036 0.051Weighting schemeb 2.336,0.002 41 1.291, 0.008 72Highest peak in 0.96 2.93difference maple A-3Largest shift1e.s.d.0.05 0.02R = ClCIF,I - I~,1]11W',I~ R' = Vw(lF,I - I ~ c I ) 2 1 ~ ~ I ~ o 1 2 1 ' ~ w =k/Co2(Fo) + sFo21.[Os,H(CO)lo(p-L2)] and 4.1% for [Os,H(CO),(p3-L')]) andthe data were corrected accordingly.Empirical absorptioncorrections were based on y~ scans with minimum and maxi-mum corrections of 0.581, 1.000 and 0.475, 0.996 beingcalculated for [OS,H(CO)~,(~-L~)] and [Os,H(CO),(p3-L2)]respectively. Structure solutions were obtained by Pattersonand Fourier methods and refinement was by the full-matrixleast-squares method. 37 Atomic scattering factors for 0 s werefrom the listings of Cromer and Mann,,, anomalous dispersionterms were from Cromer and Liberrnan.,, All non-hydrogenatoms were refined assuming anisotropic thermal motion.Phenyl-ring hydrogen atoms were placed in calculated sites(C-H 0.96 A) and were constrained to ride on their associatedcarbon atoms with overall isotropic thermal parameters refinedfor each ring.The approximate location of the bridginghydrogen in each cluster was located on a difference electron-density map but its position was not refined. The thermalparameters with these H were fixed. A similar procedure wasadopted for N(H 1) in the two clusters.Additional material for both structures available from theCambridge Crystallographic Data Centre comprises H-atomcoordinates, thermal parameters and remaining bond lengthsand angles.Photolysis Experiments.-Photolysis experiments at 366 nmwere performed with an Ealing Corporation 200 W medium-pressure mercury lamp using an interference filter (bandpass 10nm) to isolate the excitation wavelength. Solutions were filteredthrough a 0.22 pm millipore filter, deoxygenated by purgingwith purified dinitrogen and maintained at 20 "C prior toirradiation. In all photolysis experiments the concentrations ofreactant and product were monitored throughout the reactionby recording UV/VIS and FTIR spectra on Hewlett-Packar6 J.CHEM. SOC. DALTON TRANS. 1994t A\-3.1 1 T I3.2 3.3 3.4 3.5 3.6 3.71 0-3 T -W8450A UVjVIS and Nicolet 20 SXC FTIR spectrophotometersrespectively. During photolysis, samples were stirred to ensurehomogeneous light absorption by the solution. Incident lightintensities at 366 nm were determined by ferrioxalatea~tinometry.~'Photochemical quantum yields, CD, were determined bymonitoring the disappearance of the reactant complexes at theirrespective absorption maxima and by application of equation(1) which accounts for the changing degree of light absorptionand for inner-filter effects.Here, [R] is the concentration of thereactant complex at varying photolysis time t, I, is the intensityof the incident light per unit solution volume, cR and D are themolar absorption coefficients of the reactant complex and thesolution optical density at the photolysis wavelength respec-tively, b is the cell path length and CD is the reaction quantumyield. Plots of ln[(Dt - D,)/(D, - D,)] us. j:; [(l - lo-")/Dldt, where D,, D, and Do are the optical densities throughoutthe photolysis sequence at the reactant's absorption maximum(327 nm for [Os,H(CO),,(p-L')] and 326 nm for [Os,H-(CO)lo(p-L2)]) gave straight lines of slope - CDZ,&,b.Obtainedquantum yields were found to be reproducible to within 10%.Apparent activation energies (E,*) were obtained from plots ofIn 0 us. 1/T using values of CD determined over the temperaturerange 273-303 K (Fig. 4).AcknowledgementsWe thank Massey University for the award of a Ph.D.Postgraduate Scholarship (to S. L. I.), Mr. P. Loveday,University of Cambridge, for the preparation of [OS,(CO),~]and Mr J. Allen, Horticulture and Food Research Institute ofNZ Ltd., for mass spectra.References1 E. G. Boguslavskii, A. A. Shklyaev and V. F. Anufrienko, Izu. Sib.2 P. G. Antonov, Y. N. Kukushkin, V. I. Konnov, V. A. Varnek andOtd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1980,5,50.G. B.Avetikyan, Koord. 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