J. CHEM. SOC. DALTON TRANS. 1991 1855Some Reactions of Tetrakis( tert-butyl imido)osmium (viii) .X-Ray Crystal Structures of Os( NBut)O(O,CBut),( NH2Buf),.BufCO,H, ( ButN),0s( p-N Buf),Os( N But)X, (X = CI or I)and [0s2(NBut),(p-NBut),]l3tAndreas A. Danopoulos,a Geoffrey Wilkinson,*Ia Bilquis Hussain-Batesb andMichael B. Hursthouse * l ba Johnson Matthey Laboratory, Chemistry Department, Imperial College, London S W7 2A Y, UKChemistry Department, Queen Mary and Westfield College, London E l 4NS, UKReactions of Os(NBu'), with carboxylic acids and halogens have been studied. Acetic and pivalicacids give different 0x0 carboxylate complexes, the acetate being Os( NBu')O(O,CMe-0) (0,CMe-00') -(NH,Bu') 1 and the pivalate O~(NBU')O(O,CBU'-O),(NH,BU'), 2. The osmium(v1) compounds(ButN),Os(p-NBu'),Os(NBu')X, (X = I, 3; or CI, 5) have been obtained by interaction of Os(NBu'),with, respectively, I, and PPh,l in l,2-C2H,CI,; the iodine reaction also produces the paramagneticmixed-valence diosmium(v1, VII) compound [Os,( NBu'),(p-NBu'),] I, 4.The X-ray crystal structuresof compounds 2-5 have been determined: 2 is octahedral with trans- NH,Bu' and trans-carboxylategroups; 3 and 5 are isomorphous with tetrahedral and trigonal-bipyramidal osmium atoms, the latterhaving trans-halogens, a linear NBu' and two NBu' bridging goups. Compound 4 is similar to thedimeric compounds previously described and completes the series [Os( NBU'),(~-NBU')],~.+~~+.The synthesis and some reactions' of Os(NBu'), have beendescribed.Additional reactions with carboxylic acids andhalogens are now reported, and structures of some of thecompounds formed have been determined by X-ray diffraction.Analytical and physical data for new compounds are given inTable 1.Results and DiscussionReaction of Os(NBu'), with Carboxylic Acids.-Acetic andpivalic acids in dichloromethane react rapidly at low temper-ature with Os(NBu'), to give the respective osmium(v1)compounds, Os(NBut)0(02CMe),(NH2But) 1 and Os(NBu')-O(O,CBu'),(NH,Bu'),~Bu'CO,H 2. The compounds are bothvery soluble in hexane and in diethyl ether and consequently onthe small scale of synthesis used the high solubility makes itdifficult to get yields of crystals of more than ca. 20% althoughthe overall yield is higher.Propionic and butyric acid reactsimilarly but the products are oils.The acetate 1 has been characterised only spectroscopicallysince suitable crystals for X-ray study could not be obtained.The data indicate the structure 1 with both unidentate andbidentate acetate groups. The mass spectrum shows the correctmolecular ion in addition to ions corresponding to loss of But, 0and MeCO, groups. The IR spectrum can be assigned usingstandard criteria2 and comparison with data for the ion cis-[ 0 ~ 0 , ( 0 ~ C M e ) , ] - ; ~ the bands at 1581 and 1636 cm-' can beassigned to the asymmetric stretches of unidentate and chelateacetate, respectively.The structure of the pivalate 2 has been determined by X-raycrystallography and a diagram of the molecule is shown in Fig.Table 1 Analytical and physical data for the osmium compoundsCompound1 Os(NBu')O(O,CMe),2 Os(NBu')O(O,CBu'),(NH , But)(NH,Bu'),*Bu'CO,H3 OS,(NBU')~(~-NBU')~I~4 [OS,(NBU'),(~-NBU'),II,5 OS,(NBU'),(~-NBLI'),CI,Analysis (%) *Colour M.p./"C C H NOrange 140-145 32.3 5.8 7.7(decomp.) (32.3) (5.8) (6.7)Orange 78-80 44.5 8.3 5.5(44.9) (8.2) (5.8)Red 224--225 24.3 4.7 6.9(24.3) (4.6) (7.1)Red 142-145 24.4 4.6 7.1(24.3) (4.5) (7.1)Red- >240 30.0 5.6 8.7black (29.8) (5.4) (8.7)* Calculated values in parentheses. For mass spectra see Experimentalsection.1 21; bond lengths and angles are given in Table 2.The moleculargeometry is octahedral with a trans,trans,trans disposition of the0x0, imido, two monodentate carboxylate and two amineligands.The interbond angles are all within a few degrees ofidealised values. Particular features of the geometry worthy ofcomment are the trans disposition of the two n-bonding imidot Bis(tert-butylamine)(tert-butylimido)oxobis(pivalato-lcO)osmium- and oxoligands (see below), the shorter 0 s 5 N us. 0 s 5 0 bonds,pivalic acid (l/l), bis(p-tert-butylimido)tris(tert-butylimido- reflecting the greater n-donating capability of the organoimido1~N,2~~N)-dichloro-2~~Cl (or -diiodo-2~~1)~diosmium and bis(p-tert- function, and the proximal arrangement of the unco-ordinatedbuty1imido)-bis[bis(tert-butylimido)osmium] triiodide. carboxylate carbonyl oxygens. This latter feature is logicallySupplementary data available: see Instructions for Authors, J. Ckm.explained by hydrogen bonding between these two oxygens andSuc., Dalton Trans., 1991, Issue 1, pp. xviii-xxii. one of the amine donors [N(2)], where the distance1856 J. CHEM. SOC. DALTON TRANS. 1991N(24? O(11) zFig. 1 The structure of Os(NBu')O(O,CBu'),(NH,Bu'), 2 Fig. 2 The structure of (Bu'N),0s(p-NBu'),0s(NBu~)12; the chlorideanalogue is isostructural but does not show the methyl disorder at C(3)and C(5)Table 2 Selected bond lengths (A) and angles (") for Os(NBu')O(O,-CBu') , (Bu'NH 2) , 2O( lO)-Os 1.761(6)O(2tOs 1.9 57( 6)N(2)-0~ 2.088(7)C(O1)-0(1) l.258(8)C( 1)-N( 1)C( 3)-N( 3)1.5 18( 10)1.43 6( 9)O(1)-0s-O( 10)O(2)-0s-O( 1)N( l)-Os-O( 1)N( 2)-0~-0( 10)N( 2)-0~-0( 2)N( 3)-0~-0( 10)N(3)-0~-0(2)N(3)-Os-N( 2)C( 1)-N( l)-OsC( 3)-N(3)-0~8 8.7( 3)172.1(2)92.5(3)92.7(3)9 1.7(3)177.4(2)91.9(3)88.1(3)129.7(5)176.2(5)O(1)-0s 1.972( 6 )N(lkOs 2.098(7)N(3)-0~ 1.749(7)C(O2)-0(2) 1.29 l(8)C(2)-N(2) 1.522(10)0 (2)-0s-0 ( 1 0)N( l)-Os-O( 10)N( 1)-0~-0(2)N(2)-0~-0( 1)N(2)-Os-N( 1)N(3)-0~-0( 1)N(3)-Os-N( 1)C(O2)-O( 2)-0sC( 2)-N (~)-OS85.6( 3)8 5.5( 3)8 1.6(3)94.1(3)173.1 (2)93.6(3)126.8( 5)125.2(5)9333)O(11) N(2) and O(21) - N(2) are ca. 2.7 A. Hydrogen-atom positions were not confirmed, however. Hydrogenbonding also occurs between the pivalic acid molecule ofcrystallisation and the complex. Relevant interactions are fromthe protonated carboxylate on the acid to the 0x0 function onthe complex, O(100) O(10) 2.54 (1) 8, and from the acidcarbonyl to the co-ordinated amine not involved in intra-molecular hydrogen bonding, with O(200) N(l) 2.82(1) A.For both compounds the trans-imido 0x0 structure forosmium(vI), d2, is most likely for electronic reasons and resultsin a diamagnetic 18e system.The mechanism of the formation ofthese osmium(v1) compounds is not clear. Reaction (1) inScheme 1 could generate water which then leads to initialhydrolysis of Os(NBu'), as in equation (2). Hydrolysis of2MeC02H - (MeC0)20 + H 2 0 (1)0-HH20 NH~Bu'(Bu'N)~OS - (BU~N)~&$--~ - OsO(NBut)3 (2)Scheme 1ButOs(NBu'), in CH,CI, has been found' to give 0x0 imidospecies and similar replacements of imido groups by 0x0 groupson hydrolysis are known for tungsten 5a and molybdenum 5 bcompounds.However, while protonation of the lone pairs onthe bent Os=NBu' groups of Os(NBu'),. by the carboxylic acidcould lead to NH,Bu' and an intermediate with a 0s-NHBu'group and having ionic or, more likely, co-ordinated carboxy-Table 3 Selected bond lengths (A) and angles (") for (Bu'N),Os(p-NBu'),Os(NBu')X, (X = I, 3; or C1,5Compound 3Os( 1)-Os( 1)X( 1)-Os( 1)X(2)-OS( 1)N( l)-Os( 1)N( ~)-OS( 1)N(S)-Os( 1)N( 1)-0~(2)N( 2 ) - 0 ~ (2)N( ~)-OS( 2)N(S)-Os(2)C(l)-N( 1)C(2)-N(2)C(3)-N(3)C(4)-N(4)C(51-W)X( 1)-Os( 1)-0s(2)X(2)-0s( 1)-0s(2)X(2)-Os(l)-X( 1)N( 1 ) - 0 ~ ( 1)-0~(2)N( l)-Os( 1)-X( 1)N( ~)-OS( 1)-X(2)N(4)-0~( 1 )-0~(2)N(4)-0~( 1)-X( 1)N(4)-0~( 1)-X(2)N(4)-0~( 1)-N( 1)N(5)-0~( 1)-X( 1)N(5)-0~( 1 )-X( 2)N(5)-0~( 1 )-N( 1)N(S)-Os( 1)-N(4)N(2)-0~(2)-N(1)N(3)-0~(2)-N( 1)N(3)-0~(2)-N(2)N( ~)-OS( 2)-N( 1 )N( 5)-0~(2)-N(2)N(5)-0~(2)-N(3)Os(2)-N( ~)-OS( 1)C( 1 )-N( l)-Os( 1)C(l)-N(l)-Os(2)C( 2)-N( ~)-OS( 2)C( 3)-N( 3)-0~(2)C(4)-N(4)-0~( 1)0~(2)-N(5)-0~( 1)C(S)-N(5)-0s( 1)C (5)-N( 5)-0 s (2)2.749(4)2.783(5)2.719(5)1.987(26)1.610(23)2.020( 26)1.848(26)1.716(21)1.7 19(24)1.874(22)1.434(32)1.45 l(33)1.5 7 3( 39)1.455(32)1 .554(37)89.9(2)91.0(2)177.9( 1)42.2(7)89.0( 7)90.3(7)176.5(8)87.6(9)91.6(9)140.2(10)89.2(7)92.8(7)85.1(10)134.4( 10)116.1(11)113.8(10)109.6( 12)93.5( 11)114.3(9)108.6( 12)91.6(11)131.8( 18)136.6( 19)166.8(23)167.6(22)176.1(23)89.8( 10)134.5(19)1 3 5.8 (20)52.740(4)2.409(8)2.377(8)1.939( 17)1.646( 19)1.92 5 (20)1.877(16)1.79 l(18)1.689(22)1.87 l(20)1.497(27)1.338(27)1.445(33)1.5 12(28)l.S08(3 1)88.4(2)90.9(3)177.5(2)43.2(4)8 8.3 ( 6 )89.6( 6 )174.6(6)92.4(7)8 8.5( 7)142.1 (7)89.8( 7)91.3(7)86.2(8)13 1.7(8)113.2(8)114.6(9)110.6( 10)89.6(8)114.4(9)1 13.1( 10)91.8(7)134.0( 12)134.1( 13)162.7( 17)173.9( 19)169.1( 15)92.4(9)1 34.4( 15)133.1( 15)late groups, some form of two-electron reduction to Osv' is stillrequired, One possibility is that there is a reductive eliminatioJ.CHEM. SOC. DALTON TRANS. 1991 1857of Bu'HN groups from 0sv1'I to give the hydrazine (Bu'HN),.We are unaware of any precedent for such reductive eliminationand further studies on the course of the reaction are in progress.Reaction of Os(NBu'), with Iodine and PPh,I in CH2C12.-Interaction of Os(NBu'), with iodine in CH,CI, leads to twoproducts 3 and 4 that can be easily separated on account of theirdifferent solubilities in organic solvents.Spectroscopic andX-ray study confirms the structures 3 and 4 where the osmiumoxidation states are VI,VI and VI,VII respectively. The chlorineFig. 3 The structure of [OS~(NBU')~(~-NBU')~]+ in the triiodide saltTable 4 Selected bond lengths (A) and angles (") for [0~,(NBu')~(p-NBu'),]13 4N( l)-Os( 1) 1.925(10) N(3)-0~( 1) 1.71 l(8)W)-N(1) 1.496(12) C(3)-N(3) 1.4 15( 10)1(1)-1(2) 2.910(4) OS( l)-Os( 1 B) 2.921 (4)N(3)-0s(l)-N(l) 113.4(4) C( 1 )-N ( l)-Os( 1) 1 3 3.7 (7)C(3)-N(3)-0~(1) 171.2(7) N(3)-0s(l)-N(3B) 117.7(4)N( l)-Os( 1)-N( 1 B) 81.8(3) N(3)-Os(l)-N(lB) 112.6(4)N(l)-Os(l)-N(3B) 113.4(4) Os(l)-N(l)-Os(lB) 98.2(3)C( 1)-N( l)-Os( 1B) 128.1(7) I(2)-I(1)-I(2B) 180.0(3)analogue of 3, compound 5, has been obtained by the inter-action of Os(NBu'), in 1,2-dichloroethane with tetraphenyl-phosphonium iodide, where the chlorine in the product isderived from the solvent.3 4The osmium(v1) dimers 3 and 5 are moderately air-stable anddiamagnetic.Formally they can be derived from the previouslystructurally characterised osmium(v1) dimer [Os(NBu'),(p-NBu')],, by replacement of one terminal tert-butylimido groupby two halogen atoms.It may be noted that removal of a Bu'Ngroup by chlorine has been observed in the 'reductive halogen-ation' of CrV1(NBu'),CI, to give CrV(NBu')C1,.6The structure of compound 3 is shown in Fig. 2 and that of 4in Fig. 3; bond distances and angles are given in Tables 3 and 4.Compounds 3 and 5 are isostructural in the non-centrosym-metric space group P2,, although the molecules haveapproximate mirror symmetry [the plane containing C(41),C(4), N(4), Os(l), Os(2), N(1), N(5), C(l) and C(5)l. In 3 there isdisorder in two of the tert-butyl groups which does not occur in5. This molecular symmetry is arbitrarily oriented to themonoclinic axis, however. One of the osmium atoms, Os(2), hasthe tetrahedral geometry found in the neutral dimer mentionedabove, but the geometry of Os(l), where the dihalogen/imidosubstitution has occurred, has changed considerably todistorted trigonal bipyramidal.The two halogen atoms aremutually trans and axial and the main distortion is in theequatorial N, plane where the Os,N, ring structure requires amuch reduced (from the ideal 120") N(1)-Os(1)-N(5) angle of85". The substitution of one bivalent imido function by thetwo halogens has not led to the expected cis arrangement.The osmium-imido bonding shows considerable differences.The equatorial 0s-N bond distance of the terminal tert-butylimido ligand on the trigonal-bipyramidal Os( 1) centre ismuch shorter than those of the two terminal ligands ontetrahedral Os(2), highlighting the much stronger n-bondingpossibility in the former case.On the other hand, the 0s-N-0sbridges are strongly asymmetric, with much shorter bonds toTable 5 Crystal data, details of intensity measurements and structure refinementCompound 2 3Molecular formulaMCrystal systemalAb jACIAEl" PI"Ti"UIA3Space groupZDJg ~ m - ~p1cm-IF(W0)Total no. of reflectionsNo. of unique reflectionsNo. of reflections used [F > 3n(F)]No. of parametersWeighting scheme parameter g inFinal RFinal R'W' = l/[d(F) + gF2]C22H49N3050s'CSH902690.94Monoclinic18.693( 3)10.262(3)19.390(5)90118.87(2)903284.9941.39737.2214205355486841084160.000 29P21ln0.02630.0274C20H4512N50s2989.82Monoclinic10.129(2)10.697(3)15.249(2)90103.98(1)901603.2822.050193.0591630952974236028 1Unit weightsp2,0.03980.039841187.85Monoclinic1 1.544( 1)14.339( 1)12.738( 1)90107.54( 1)901955.35C2/m22.01 8154.381102566818311536910.010 23C24H5412N60s20.04770.04905806.92Monoclinic10.158(2)10.6 1 6( 3)14.526( 5 )90104.6 l(2)901513.5321.771204.49727299 1283 1245226 10.003 28c2 OH4SC12NS0s2p2 10.05220.0531858 J.CHEM. SOC. DALTON TRANS. 1991Table 6 Fractional atomic coordinates ( x lo4) for Os(NBu')O(O,CBu'),(Bu'NH,),*Bu'CO,H 2Atom X Y Z Atom X2562.7( 1)2692(3)1848(3)3192(3)161 9(3)2446(3)738(4)4 120(4)2403 (5)708(5)3595(3)375(5)333(5)45 19(5)478 5 ( 5 )3606(5)1645(6)3 158(6)233 l(8)2150.0(2)2144(4)368 1( 5)528(4)827(5)3279(5)2082(5)1093( 8)3857(7)1983(7)19 15(8)17 13(9)28 3 3 (9)4579(9)4721(7)2693( 10)25 5 3( 10)581(10)- 155(9)244.0( 1)- 596(3)- 194(3)533(3)- 385(3)890(3)1085(3)571(4)1802(5)- 956(4)- 1616(4)-491(6)- 1290(6)337(6)1264(5)1 70 1 (6)1945(7)- lOl(4)2444(5)1938(4)1308( 5)2438(3)1575(5)458(5)1273(7)3 857(4)4159(5)42 17(3)4782(9)4529( 1 1)3442(8)6984(4)7970(4)7483(5)7384(5)6923(8)8228(6)6965(9)Y4684(7)5688(7)4859(5)6241(8)5 12 1 (10)6666( 10)309(7)1045(5)- 1001(7)- 1286(12)- 1080( 16)- 1899(10)- 473(5)453(7)584(6)1377(7)2465( 10)1 854( 12)761(11)z21 8(4)897(3)- 283(4)- 854(6)- 778(7)280(6)1172(4)122 l(5)1696(3)2080(7)693(9)953( 1 1)137 l(4)139 l(5)1610(4)2147(4)1653(7)2706(7)2 577(7)Table 7NEu'),Os(NBu')I, 3Fractional atomic coordinates ( x lo4) for (Bu'N),Os(pX8 083(1)6 927( 1)7 511(2)8 579(3)6 253(24)6 793(18)6 321(24)8 809(23)8 699(20)4 953(24)6 565(35)5 542(35)9 377(36)10 078(32)5 061(38)4 458(28)3 927(28)7 054(31)5 061(39)7 315(48)8 593(39)10 595(40)10 235(38)11 051(35)10 595(37)9 835(55)9 923(61)6 112(58)4 025(42)4 648(65)5 982(55)Y01 767( 1)1487(2)-1 517(3)40 1 (24)1712(24)3 175(20)1543(25)1958(34)4 434(29)2 239(35)- 966(22)- 184(23)- 1 887(34)- 1 257(36)- 624(33)756(34)3 147(32)978(48)1800(44)- 2 445(43)- 2 439(43)- 976(42)1 649(49)1478(44)3 547(55)3 435(66)5 358(60)4 245(43)4 185(63)4 910(53)Z2 077( 1)2 968( 1)534(1)3 551(2)2 258( 14)4 068( 13)2 494( 16)1533(14)2 829(13)1932(18)4 956(19)2 192(24)1024(22)3 150(24)1286(28)2 747(20)1384(23)5 272(22)4 863(22)5 636(32)289(30)1697(29)424(25)2 672(28)4 174(25)2 706(44)3 573(48)2 934(41)2 173(34)1267(48)1380(38)I II>I' x xI IRN-M" [RN-M" J'X-rn JYtetrahedral Os(2) than to Os(l), with canonicals of the form Iand a representation as 0 ~ ~ ~ 0 s ~ ~ ~ ' rather than OsvlOsvl, or 11,Table 8NBu'),]I, 4Fractional atomic coordinates ( x lo4) for [Os,(NBu'),(p-Atom X Y Z301.7(4)3270(2)50001 1 l8(9)468(7)2425( 11)3257( 15)2696( 12)707( 11)1969(16)36(21)- 37(24)000000900( 10)- 1021(7)- 1784(8)- 1905(14)- 2606(15)- 1635(18)123.4(4)6290(2)50001981(8)127(13)1427( 19)2742( 11)3274(20)2143(22)3497(21)89(9)- 340( 18)which retains the Osv'Osvl distribution.For both I and 11,however, the tetrahedral osmium atom has access to an excess of18e if all the imido groups were to use their full n-bondingcapability as shown. It is pertinent to note that all the terminalimido groups are linear, consistent with some contribution fromthe 4e bonding mode Bu'NSOs.In the structure of compound 4 both anion and cation lie onpositions of symmetry 2/m.For the cation the mirror plane iscoincident with the Os,N, ring. Thus the two osmium atomsare crystallographically and structurally equivalent. Thecomplex is formally a mixed-oxidation-state OsvlOsv" system,and falls between the previously described neutral Osv'Osvland dicationic 0 ~ ~ ~ ~ 0 s ~ " com lexes. For the neutral complex,direct Os-0s bonding is postulated, 2.68 A. In the presentmonocation 4 the distance is 2.921(4) A. The bridges aresymmetrical and the bridging and terminal Os-N distances aresimilar to those in the dication. Compound 4 shows no NMRspectrum, being paramagnetic with a magnetic moment (byEvans' NMR method) corresponding approximately to oneunpaired electron per cation. The 13- ion is linear andsymmetrical by virtue of crystallographic site symmetry.The mechanism of the reaction of Os(NBu'), and I, is notclear.Initial free-radical or polar additions of halogen acrossM-N bonds would form intermediates of the type 111 or IV thatcould decompose by different pathways such as substitution byhalide followed by reductive elimination as in Scheme 2.Dimerisation of reactive intermediates would give the products;for 4, these would have to be in non-equivalent oxidation states.There is no evidence for the mixed-oxidation-state species 4 inthe cyclic voltammograms of either [OsV'(NBut),(p-NBut)1,the Os-0s distance was 3.1 s: and in the dication, in whicJ. CHEM. SOC. DALTON TRANS. 1991 1859Table 9NBu'),Os(NBu')Cl, 5Fractional atomic coordinates ( x lo4) for (Bu'N),Os(pX8 335(1)7 214(1)7 884(7)8 678(7)6 538(15)7 008( 17)6 632(21)9 150(18)8 965(20)5 148(23)6 674(22)6 125(27)9 754(21)10 341(25)5 310(27)4 648(28)4 221(27)7 266(31)5 172(33)7 338(30)6 621(32)4 552(31)6 586(31)8 679(28)10 447(29)10 515(28)1 1 315(31)11 037(32)10 454(31)Y01 752(1)1411(6)- 1 412(7)390( 15)1555(18)3 178(20)1401(18)1746(25)4 430(26)1979(27)- 1 002(17)- 145(23)- 1 800(21)- 1 329(27)- 698(28)814(27)732(31)2 104(32)3 287(30)5 410(32)4 397(32)4 662(31)- 2 442(28)- 2 830(29)- 98 l(27)1888(33)1225(32)2 796(33)z2 072( 1)3 035( 1)728(4)3 383(5)2 229( 10)4 216(12)2 595(15)1 548( 13)2 908( 14)1826(16)5 039( 15)2 321(20)895(16)3 335(19)1161(19)2 678(21)1238(21)5 813(24)4 930(26)5 426(22)3 190(25)2 033(26)1330(24)13 l(22)1562(22)345(21)2 847(21)4 253(26)4 173(27)\ RN-M"Scheme 2or [OS~"(NB~'),(~-NB~')],~+, nor can 4 be obtained bychemical reduction of Os(NBu'), or oxidation of [Os(NBu'),-The interaction of the halides 3 and 5 with silver oxidegives rise to the tetraosmium compound [(Bu'N),Os(p-NBu'),-Os(NBu')(p-O)], that has been previously structurallycharacterised. Both 3 and 5 are also reduced by sodiumamalgam in tetrahydrofuran (thf) to a neutral compound,Os,(NBu'),, identical to that produced by interaction ofOs(NBu'), with trimethylphosphine.This compound will bedescribed separately.(P-NBU')Iz.ExperimentalThe general techniques used and instrumentation have beende~cribed.~ Analyses were by Pascher, Imperial College andUniversity College, London.Mass spectra were recorded byelectron impact, NMR spectra in CDCl, vs. SiMe, and IRspectra in Nujol mulls unless otherwise specified. The synthesisof Os(NBu'), has been described.' All reagents were thoroughlydried and all operations were carried out in vacuum or underpurified Ar or N,.Reaction of Os(NBut), with Carboxyfic Acids: (Acetato-KO)(acetato-K 20,0')(tert-butyZamine)( tert-butyfimido)oxo-osmium( VI) 1 and Bis( ter t -bu tyZamine)( t ert -bu tylimido)oxo-b i s ( p i v ~ l ~ t o - ~ O ) ~ ~ m i u m ( ~ ~ ) 2.-To a solution of Os(NBu'),(0.4 mmol) in CH,Cl, (10 cm3) at -78 "C was added onexcess of either anhydrous acetic or pivalic acid (ca.0.2 cm3).The orange-brown solution which became red-brown wasallowed to warm to room temperature, stirred for ca. 1 hwhen the volatiles were removed in vacuum. The residue waswashed with hexane, dissolved in the minimum of diethylether which was filtered, then concentrated and cooled(- 20 "C) to give orange crystals of compound 1 or 2 in yields15-20%. Mass spectrum of 2: m/z 513 ( M - Bu'CO,H), 497( M - Bu'C0,H - 0), 457 ( M - Bu'C0,H - Me,MH,)and 442 (M - Bu'C0,H - NBu'). IR of 1: 1636, 1581, 1558,1400 [C(O)O]; 1207 (NBu'); and 928 cm-l (OsO). NMR: 'H, 1,6 2.16 (s, 6 H, O,CMe), 1.75 (s, 9 H, NH,Bu') and 1.50 (s, 9 H,NBu'); 2, 6.13 (s, br, NH,Bu'), 1.41 (s, 18 H, O,CBu'), 1.28 (s, 9H, Bu'N), 1.23 (s, 9 H, 0,CBu') and 1.19 (s, 18 H, NH,Bu').In the acetic acid reaction some blue crystals were depositedinitially on warming to room temperature but attempts torecrystallise these very air-sensitive crystals led only todecomposition.Reaction of Os(NBu'), with Iodine: Bis(p-tert-butyl-imido)tris(tert-butyfimido-l~N,2~~N)diiodo-2~~I-diosmium 3and Bis(~1-tert-butylimido)-bis[bis(tert-butyfimido)osmium]Triiodide 4.-To a solution of Os(NBu'), (0.4 mmol) in CH,Cl,(10 cm3) was added I, (0.25 g, excess) and the dark brownsolution stirred (2 h) then evaporated in vacuum.Excess ofiodine was sublimed to a cooled probe (solid CO,) and theresidue extracted with hexane (2 x 30 cm3); the extracts werefiltered, concentrated (to ca. 5 cm3) and cooled (- 20 "C) to givered crystals of compound 3 in ca.40% yield. The residueinsoluble in hexane was extracted into dichloromethane (ca. 10cm3), filtered and layered with Et,O. Diffusion for 24 h affordedred crystals of compound 4 in ca. 30% yield. Mass spectrum of 3:m/z 735 (A4 - I,), 679 (M - I, - Me,C==CH,) and 664 (M -I, - NBu'). IR: 3, 1288, 1202, 1183 (NBu'); 4, 1220 and 1205cm-' (NBu'). NMR of 3: 6 1.91 (s, 9 H, terminal NBu'), 1.89 (s, 18H, p-NBu') and 1.41 (s, 18 H, terminal NBu').Bis( p-tert -bury h i d o ) tris(tert-butylimido- 1 KN,~K,N)-dichloro-2~~Cl-diosmium 5.-To a solution of Os(NBu'), (0.5mmol) in 1,2-dichloroethane (10 cm3) was added PPh,I (0.23 g,0.5 mmol) and the mixture refluxed (12 h) when the colourchanged from orange-brown to green.After evaporation invacuum the residue was extracted with hexane until the extractswere colourless (5 x 20 cm3); the combined extracts werereduced in volume (10 cm3) and cooled (- 20 "C) to afford darkred dichroic prisms. Yield: ca. 60%. Mass spectrum: m/z 770(M - Cl), 735 ( M - 2C1) and 664 (M - 2C1 - NBu'). IR:1231, 1200 (sh) and 1189 cm-' (NBu'). NMR: 6 1.84 (super-imposed peaks, 27 H, NBu', bridging and terminal) and 1.40(s, 18 H, terminal NBu').X- Ray Crystaflography .-Notwit hs tanding the air stability ofsome of the compounds, crystals used. for X-ray work weresealed in thin-walled glass capillaries under argon. Unit-cell andintensity data for compounds 2,3 and 5 were obtained using aCAD4 diffractometer, following published procedures.8 Theintensity data were corrected for absorption using yr-scanprofiles.Data for compound 4 were obtained using an Enraf-Nonius FAST area detector diffractometer. Full details of theprocedures used will be published separately, but the mainfeatures are summarised as follows.With detector-to-crystal distance (d.e.t.) of 40 mm and ascanning angle ( = 28,) of 18", reflections were found in two 5" orotation regions separated by 90". The orientation matrix andunit-cell dimensions were determined via the INDEX andREFINE procedures of the SADONL software (the 'smallmolecule' on-line version of MADNES '), using 250 reflectionstaken from both regions. Accurate values of d.e.t.and 28, werealso determined by refinement as 40.55 mm and 17.95". Intensitydata corresponding to slightly more than one hemisphere ofreciprocal space were recorded using two o rotations of loo",with a 90" cp shift, at x = 0" and two further o rotations of 70",again with a cp shift of 90" at x = 90" to record the cusp data.Throughout the data collection the o step was 0.15" and thJ. CHEM. SOC. DALTON TRANS. 1991frame measuring time was 20 s. The structures were solved viathe heavy-atom method and refined by least squares.Absorption corrections were applied at the isotropic refinementstage using the DIFABS lo procedure. All atoms were refinedanisotropically and no hydrogen atoms were included. Crystaldata and further experimental details are summarised in Table5.Final atomic coordinates are given in Tables 6-9.Additional material available from the Cambridge Crystal-lographic Data Centre comprises thermal parameters andremaining bond lengths and angles.AcknowledgementsWe thank the SERC for support and provision of X-ray facilitiesand we are indebted to Johnson Matthey plc for a loan ofosmium tetraoxide.References1 A. A. Danopoulos, G. Wilkinson, B. Hussain-Bates and M. B.2 K. Nakamoto, Infrared and Raman Spectra of Inorganic andHursthouse, J. Chem. SOC., Dalton Trans., 1991,269.Coordination Compounds, 3rd edn., Wiley-Interscience, New York,1978.3 T. Behling, M. V. Capparelli, A. C. Skapski and G. Wilkinson,Polyhedron, 1982, 1, 840 and refs. therein.4 W. A. Nugent and J. H. Mayer, Metal-Ligand Multiple Bonds,Wiley-Interscience, New York, 1988; R. H. Holm, Chem. Ret;., 1987,87,1401; K. Tatsumi and R. Hoffmann, Inorg. Chem., 1980,19,2656.5 (a) A. A. Danopoulos, G. Wilkinson, B. Hussain-Bates and M. B.Hursthouse, J. Chem. SOC., Dalton Trans., 1990, 2753; (b) M. L. H.Green, G. Hogarth, P. C. Konidatis and P. Mountford, J. Chem.SOC., Dalton Trans., 1990, 3781.6 A. A. Danopoulos, B. Hussain-Bates, M. B. Hursthouse, W.-H.Leung and G. Wilkinson, J. Chem. SOC., Chem. Commun., 1990,1678.7 A. A. Danopoulos, A. C. C. Wong, G. Wilkinson, B. Hussain-Batesand M. B. Hursthouse, J. Chem. SOC., Dalton Trans., 1990, 315.8 R. A. Jones, K. M. A. Malik, M. B. Hursthouse and G. Wilkinson, J.Am. Chem. SOC., 1979,101,4128.9 MADNES VERSION 11-SEP-1989, J. W. Pflugrath and A.Messerschmidt, Distributed by Enraf-Nonius, Delft, 1989.10 N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect A, 1983, 39,158.Received 14th Febpuary 199 1; Paper 1 /007 1 1