Spectroscopic properties of Os(VI) monoesters containing heterocyclic nitrogen ligands

J inor~, nuc ('hem 'vol 42, pp 12Tv 128-4 Per~zamqm Press I td !~O Prinled in Great Brilain

SPECTROSCOPIC PROPERTIES OF Os(VI) MONOESTERS CONTAINING HETEROCYCLIC NITROGEN LIGANDS W. C. BRUMLEY and C. C. HINCKLEY The Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL 62901, U.S.A.

IFir~t received 24 September 1979; receivedfor publication 22 October 1979) ~bstract--A series of osmium monoesters containing heterocyclic nitrogen ligands has been prepared from bicyclic and acyclic alkenes, and IR, UV-visible, and NMR spectroscopic properties are reported. As an elaboration of the NMR properties of the monoesters, the chemical shifts of the protons of the complexes in deuterochloroform solution have been followed as a function of increasing lanthanide shift reagent concentration. Besides providing general indices to the identification of the monoesters, the observed induced shifts are consistent with the formation of a unique product from the alkene substrates even when cis/trans isomers are encountered. The observed shifts are qualitatively consistent with a structure containing the expected osmyl group with the nitrogen atoms of the ligands and the oxygens of the esterified olefin lying approximately in a plane through the osmium atom perpendicular to the osmyl group.

INTRODUCTION The preparation of osmium monoesters was reported over forty years ago by Criegee et al.[1,2]. A basic interest in high oxidation state osmium chemistry stems from use of osmium tetroxide as a cis hydroxylating reagent in organic chemistry[3]. A recent interest in osmium chemistry has centered on its importance as a fixing agent in electron microscopy and elucidation of chemical structures resulting from its fixing action[4]. Hinckley and Murphy have introduced a new stain containing Os(Vl)[5] which further extends the practical applications of osmium chemistry in electron microscopy. Kinetic studies have appeared which concern the reaction of osmium monoesters with organic substrates[6]. More recent work involves osmium monoesters prepared from catechols[7] and alkynes and dienes[8]. Despite this interest in osmium esters, little definitive structural work has appeared on these compounds with respect to single crystal X-ray diffraction studies[9, 10], although I R studies have appeared [ l l]. Solution structures of osmium esters have been inferred largely from IR studies. An NMR study of diesters has appeared[12]. In this work we offer additional spectroscopic information to aid in the identification of osmium monoesters containing heterocyclic nitrogen donor ligands generally prepared according to eqn (1) using 2,2'-bipyridyl as the ligand (bpy) R2(" - CRi 4 0 s O 4 + bpy . . . . OsO:(1L, C202)bpy.

(1)

The elemental composition of osmium bpy monoesters may be contrasted with that of osmium diesters where some similarities are apparent: OsO(R4C202)2. Included in this report are NMR data of monoesters with relative induced shift indices obtained from the association of a lanthanide shift reagent (LSR) with the osmium monoesters containing heterocyclic nitrogen ligands. Applications of shift reagent methodology to inorganic substrates have been few[13], and limitations imposed by the complexity of the analysis are discussed. EXPERIMENTAL

Reagents. All NMR reagents, solvents and alkenes (Aldrich) ~vere commercially JJy( ~1 ~?,N,,~ -~

available and used

without

further

purification except that commercial shift reagents (Willow Brook, Aldrich) were stored under vacuum desiccation over P,O,. Physical data. All commercial elemental analyses were performed by Galbraith Laboratories, Inc., Knoxville, Tennessee. Melting points were taken on a Thomas-Hoover "Uni-Melt" melting point apparatus in open capillaries and are uncorrected. Spectroscopic measurements. IR spectra were recorded on a Beckman IR-10 spectrophotometer. The spectra were calibrated with a polystyrene film. All reported frequencies (cm ~) are considered accurate to -+4 cm ~. Solid samples were run as mulls using Nujol as the mulling agent and cesium bromide salt plates. UV-visible (UV-vis) spectra were recorded on a Beckman DK-1A spectrophotometer. Solutions were measured in 1.0cm matched quartz cells (Beckman). Measurements of band positions in the UV region are considered to be accurate to within -+3 nm and those in the visible region to within -+2 nm. NMR spectra were recorded using a Varian HA-100 spectrometer operating in the HR mode. The operating resonance frequency for protons was 100 MHz. Samples were run in 5 mm o.d. (3.Smm i.d.) NMR tubes (Willmad, Ultra Precision No. 504-PP) usually at 0.1 M or slightly greater concentration. TMS was used as internal reference and as lock signal. In a typical experimental run, the normal PMR spectrum of the substrate was recorded. Thereafter, small amounts of solid LSR were introduced into the NMR tube, and the PMR spectrum was recorded after dissolution and minor retuning of the NMR instrument.

Synthetic

procedures, bpy(trans-4-methyl-2,3-pentanedio-

lato)dioxoosmium(VI) [OsO2(CIoHsN2)(C6Hi~0~)1: In a typical experiment following the procedure of Criegee[l], 0.1686 g of alkene, 0.3080g of bpy, and 0.5 g of OsO4 in benzene solution yielded 0.9005g (92.1% yield) of a brown amorphous solid (recrystallized from CDCI3/CCI4), m.p. 194-196°C w:ith decomposition. Anal. Calc. for Cl~H,,oO4N2Os: C, 38.70; H, 4.07; N, 5.64. Found: C, 38.46; H, 4.11: N, 5.53. Other compounds were prepared in a similar manner. RESULTS AND DISCUSSION The X-ray structure of K2(OsO2(OHh)[19] indicated the presence of a linear O=Os=O moiety (osmyl group) consistent with the diamagnetism of osmyl compounds expected from the stabilization of the dx~ orbital[10, 15]. More recent X-ray work has suggested a slightly bent structure (O=Os=O angle of 162°) for the osmyl group in a monoester containing two pyridine ligands [9], Griffith used IR studies of osmium oxy compounds to assign bands in the 800-900cm ' range as the asymmetric stretch of the linear osmyl group. Thus, the evidence

1277

1278

W.C. BRUMLEYand C. C. HINCKLEY

currently available suggests the presence of a linear or nearly linear osmyl group in monoesters. IR spectra IR spectra were obtained for a series of osmium monoesters and spectral assignments are given in Table I. The main diagnostic IR band for these compounds occurred as a strong absorption in the range of 819832 cm -1 and was assigned to the asymmetric stretching frequency of the osmyl group[l 1, 17]. Bands in the range of 859-872cm -I have been assigned to the symmetric stretching of the osmyl group. Other bands supported the general formulation of osmium-oxygen (ester) bonds (570-660cm-') and the presence of nitrogen donor ligands but are less diagnostic of stereochemistry. These latter assignments were made in reference to published work on characteristic bands found in free and complexed nitrogen ligands [18, 19]. The osmyl stretching frequency may be compared to the Os~O stretching vibration of diesters found in the range of 985-991cm-1120]. The higher frequency for diesters is consistent with the apparent higher Os-O (apical) bond order in the diester. The Os-O (osmyl) vibrational frequencies may be compared with other metal oxygen bonds. The cis oxygens of MoO2L2 compounds exhibit a metal oxygen frequency of ca. 900 cm-t [21], and the uranyl group in UO2(NOa')2L2 compounds is found in the range of 910-960cm-'[22]. The IR absorption frequencies of tetrahedral structures of metal tetraoxides are found in the range of 820-970 cm-t; terminally bound oxygen or nitrogen comparable to the Os-O apical bond of diesters has an IR band in the range of 860--1050cm-~ [19].

UV-visible spectra Bands observed in the UV-visible spectra are tabulated in Table 2. The chief features of the spectra are the appearance of two bands and a shoulder in the visible region (17-25 kK) and two bands and a shoulder in the UV region (32-35 kK) for most monoesters containing bpy. The visible region bands are tentatively assigned as ligand field bands due to their absence in the free ligands and their small extinction coefficients. Since the monoesters only approximate C2o microsymmetry about the Os atom, a specific assignment would be speculative. The visible bands may be compared to the three bands found in the range of 17-27kK for Os diesters[20]. The two bands in the UV region were assigned as N-donor ~r-Tr* transitions due to their similarity to free nitrogen heterocycle band positions and their large extinction coefficients. Charge transfer bands observed in diesters in the 29--36kK range are obscured by the strong UV bands of the heterocyclic ligand in the monoesters. UVvisible spectra support the presence of the nitrogen donor ligand but do not offer a straightforward means of establishing stereochemistry about the Os atom. Unshifted NMR spectra The PMR spectra contain resonances characteristic of the nitrogen heterocyclic ligand and of the esterified alkene. The proton chemical shifts of themselves do not suggest a particular stereochemistry about the osmium atom. PMR assignments in the unshifted spectra are tabulated in Table 3 where the shifts of the esterified and native alkene are compared. Proton numbers are identified by reference to Figs. 1-5.

Table 1. IR spectrM assignments (cm-~) for Os monoesters (Nujol; CsBr sMt plates) DERIVATIZED ALKENE AND LIGAND

u(O=Os=O)

v(C-Oe)

LIGAND

v(OS-Oe)

OTHER

B-plnene

825vs

I028m

1601m,969m,

~85m

859w

825vs

lO19s

1607m,773m,

660m,

872m

704s

588s

1622w,1585w,

666w,

872m

1570w,1550w

618w

854w,690w

1601m,936m,

618w

854w,690w

649w

864w,682w

585s

860m,667m

570w

867m,657~

581s

870w,642s,

bpy B-plnene

766s

bispy 8-plnene

829vs

I019m

DDphen a-plnene

819vs

1006m

825vs

t005w

bpy cls-3-methyl-

777s

2-pentene,bpy cls-4-methyl-

920m 820vs

2-pentene,bpy trans-4-

832vs

i075m,

1600m, l160w,

1038m

ll10w,950m,762s

1040m

methyl-2-pentene,bpy cls-2-octene

819vs

bpy trms-2-

octene,bpy

1601m,115Iu,

830vs

1601m,l159w, 968m,992m,770s

lO65w

1600m,l145w,

I042s

965m,944m,765vs

1060m,

1602m,l161w, L 940m,770s

1041s

726w 650m

865w,670m, 736w

Spectroscopic propertiesof Os(V1) monoesterscontaining heterocyclic nitrogen ligands

1279

Table 2. UV-visible spectral assignments (kK) for Os monoesters(CHCI~) DERIVATIZED ALKENE AND LIGAND

LIGAND FIELD (E)

INTRALIGAND (c X 10-3)

8-ptnene

17.1(54)

32.2(18.4)

bpy

21,8(124)

33.3(18.1)

24.3sh

34.6sh

~-pinene

22.0(176)

33.9(4.6)

bispy

25.0(193)

~-pinene DDphen

24.3(248)

34.4(50.4)

a-pinene

17.Ssh

32.2(20.8)

bp~

24.0(166)

33.4(20.6) 34.6sh

cis-3-methyl-2-pentene

16.9sh

32.2(19.0)

bpy

21.4(122)

33.3(19.0)

24.4(160)

34,6sh

cis-4-methyl-2-pentene

17.0sh

32.2(17.7)

bpy

21.6(114)

33.3(17.2)

24.6(150)

34.6sh

trans-4-methyl-2-pentene

17.9sh

32.2(23.0)

bpv

21.6(142)

33.4(24.0)

24.1(155)

34.6sh

cis-2-octene

17.2sh

32.2(19.8)

bpv

21.9(132)

33,3(18.8)

24.5(157)

34,6sh

trans-2-octene

16.9~h

32.2(18.0)

bpv

21.4(143)

33.3(18.8)

24.4(155)

34.hsh

The bpy resonances are generally found in the range of 7.6-9.4ppm (downfield relative to TMS). The Os bpy monoester of/3-pinene (Fig. 1) illustrates typical features of the entire series of monoesters. The two protons ortho to nitrogen of bpy (Nos. 28, 35) are individually defined in the spectrum. The other ring resonances are multiplets grouped pair-wise for the meta (external, Nos. 29,34),

para (Nos. 30,33), and meta (internal, Nos. 31,32) protons. The positions of these resonances are largely independent of the esterified alkene throughout the series of monoesters. NMR assignments of the methylene protons of the/3-pinene monoester (Nos. 46, 47) were made on the basis of LSR experiments described below. The methylene protons exhibited a marked dependence of

/'42

42 45 46

/ ,

34

O~ 29

45 46

d 30

Eu

x -

35~/4

o

37 36

2 8 ~ b

/

29

31 \

30

Fig. 1. Proposed structure and atom numbering of (a) Os Bpy monoester of/3-pinene and (b) LSR coordination characteristics.

1280

W.C. BRUMLEY and C. C. HINCKLEY Table 3. NMR assignments in unshifted spectra (CHCI3; PPM from TMS) by proton number in monoesters and comparison with native alkene OS MONOESTER, LIGAND

8-ptnene, bpy

8-ptnene,

DDphen

~-pinene, bispy

a-plnene, bpy

cl___ss-3-methyl-2pentene, bpy

cls--4-methyl-2pentene, bpy

trans-4-methyl-2pentene, bpy

cl....~s-2-octene, bpy trans-2-octene, bpy

LIGAND

ESTERIFIED ALKENE (NATIVE ALKENE]

28-9.37 29,34-7.59 30,33-8.04 31,32-8.26 35-9.30

37-1.90(1.42) 40-1.32(1.24) 41-1.08(0.73) 46-4.66(4.6) 47-4.42(4.6)

28-3.62 29,34-7.62 30,33-7.51 31,32-7.84 35-3.64

36-1.79 40-1.32 41-I .02 44-2.28 46-4.55 47-4.40

28,35,48,49-8.86 29,31,32,34-7.82 30,33-7.44

36-2.01 40-1.29 41-1.02 44-2.28 46-4.37 47-4.48

28,35-9.34 29,34-7.61 30,33-8.09 31,32-8.32

36-5.04(5.19) 43-1.10(0.84) 44-1.37(1.26) 45-1.53(1.66)

24,31-9.35 25,30-7.64 26,29-7.64 27,28-8.29

33-4.55(5.16) 34-1.59(1.68) 35-2.1(2.04) 36-0.97(0.96) 37-1.61(1.56)

21-9.33 22-7.64 23,26-8.08 24,25-8.28

29-4.79(5.26) 30-4.39(5.26) 31-1.46(1.60) 33-2.02(2.62) 34-1.15(0.94) 35-1.30(0,94)

21,28-9.36 22-7.67 23,26-8.07 24,25-8.27

29-4.10(5.37) 30-4.46(5.37) 31-1.69(1.63) 33-2.28(2.25) 34-I.12(0.96) 35-1.23(0.96) 29,30-4.59(5.42) 31-1.48(1.16) 33-2.08(2.04)

21,28-9.36 22-7.67 23,26-8.08 24,25-8.29 21,28-9.38 22,27-7.64 23,26-8.07 24,25-8.27

their chemical shifts on the particular N-donor ligand present. For the cases of the bpy, bispyridine (bispy), and 2,9 - dimethyl - 4,7 - diphenyl - 1,10 - phenanthroline (DDphen) N-donors, chemical shifts in unperturbed spectra were found to be (Nos. 46, 47) 4.66, 4.42; 4.37, 4.48; 4.55, 4.40ppm respectively. Esterification deshielded the two methyl groups (Nos. 40,41) of fl-pinene relative to their shifts in underivatized fl-pinene. We propose that the ester is attached such that the bpy ligand is as far away as possible from the bridgehead methyls (Fig. l). In the Os bpy monoester of a-pinene (Fig. 3), the bridgehead methyls (Nos. 43, 44) are again deshielded compared to unesterified a-pinene resonances, but the methyl on carbon geminal to the ester oxygen (No. 45) is more shielded than it is in a-pinene itself and similarly for the methine proton (No. 36). We propose that the ester attachment is from the far side relative to the bridgehead methyl groups (Fig. 3). Monoesters derived from open chain olefins exhibit similar trends in comparing chemical shifts of esterified

29-4.26(5.42) 30-4.40(5.42) 31-1.67(1.65) 32-2.20(2.00)

to unesterified compound. Those methyl and hydrogen moities attached at carbon alpha to the ester oxygen usually become more shielded compared to resonances found in the olefin. Hydrogens and methyl groups attached at least one carbon removed from the doublebonded carbons are deshielded in the Os monoester compared to alkene resonance positions. For example in considering the Os bpy monoester of cis-3-methyl-2pentene, the chemica/ shift of methyl No. 33 on carbon geminal to the ester oxygen (Fig. 3) is 1.59ppm compared to 1.68 ppm in the alkene. Hydrogen No. 32 gave a resonance at 4.55ppm compared to 5.16ppm in the alkene, but methyl No. 36, an additional bond removed from an ester oxygen, gave a resonance at 0.97 ppm compared to 0.96 ppm in the alkene. Methyl No. 37 was an exception to this trend.

LSR shifted NMR spectra Initial experiments with Os bpy monoesters using Eu(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedione) failed to provide appreciable induced shifts in proton

128.1

Spectroscopic properties of Os(VI) monoesters containing beterocyclic nitrogen ligands

42

42

'~

45 46

...-"

4o'~

/

'

34

ost"\ ~

~,~

" -° ' f 1 1 "

.

J

,

- ""--'~ /"• *' ' \ 3"1 "~0

2°°~

b

3~

29

30

Fig. 2. Proposed s|ructure and atom numbering of (a) Os DDphen monoester of /3-pinene and (b) Os Bispy monoester of/3-pinene.

43 44

./ 37

3~.. 34

4z 4s

"'./ /

,,.

1

35"~32 I

0

24 2~ ~

b 31-~ 34

~--28

30

33

26

29

Fig. 3. Proposed structure and atom numbering of Os Bpy monoester of (a) a-pinene and (b) cis-3-methyl-2pentene.

34

34

J

35

'"

22

2, -'-~-J~'-O 0

~l~Lo°

..,s~

~Os~ \

~23

4 b

27

7

~

2 8 ~

2"7

26

25

26

Fig. 4. Proposed structure and atom numbering of Os Bpy monoester of (a) cis-4-methyl-2-pentene and (b)

truns-4-methyl-2-pentene. resonances. Succeeding experiments employing Eu(fod)3 (fod= 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octane dione) which is a stronger Lewis acid in CDCI3 than is Eu(dpm)3 indicated that induced shift magnitudes were a function of added LSR. In consideration of the proposed structure of Os bpy monoesters involving a linear osmyl group, there appeared to be four likely sites of association consisting of

the two ester oxygens in the Os-O-C bonds and the two osmyl oxygens. Current calculation of LSR induced shifts consists of assuming a structure for the substrate molecule (i.e. the monoester) and developing coordinates from the assumed model. In a single association site problem, the various possible positions of the metal complex relative to the substrate molecule are adjusted iteratively in order to bring calculated shifts into the best

1282

W.C. BRUMLEYand C. C. HINCKLEY

C4HI

C4He

33 - ~

22

22

~24 a

zs

~

/,

,-'-its

zs

2ti

Fig. 5. Proposed structure and atom numberingof Os Bpy monoester of (a) cis-2-octene and (b) trans-2-octene. possible agreement with observed shifts with a given parameterization. Induced shifts are calculated assuming a case of axial symmetry about the LSR-substrate bond using the first term of eqn (2)[23]. A-

-/3

cos 2 0~\

vdv°=D'[7)+O2[

_ / s i n 20~ cos 2II~'~

'

ri3

]

(2)

or by using both terms in non-axially symmetric cases[24]. At present some controversy surrounds the relative merits of using bound shifts or relative shifts for the experimentally derived LSR induced shifts[25]. A recent paper has critically evaluated the various experimental and analytical approaches used in arriving at experimental values for bound shifts in the presence of 1 : I and 2: 1 weak molecular complexes (substrate:LSR)[26]. Complications arise in the association problem involving two or more sites in terms of the total number of variable parameters necessary to fit calculated to observed shifts in the context of a limited number of observable proton resonances. Rather substantial uncertainties exist as well with inorganic substrates in terms of the bond lengths and angles to be assumed for the trial structure if accurate X-ray data are not available. With most organic substrates, the angle 0 defined by the proton-association site-lanthanide system (0 in eqn 2) falls in a range less than 54.70 (a zero of the function in the first term of eqn (2), the so-called magic angle). With inorganic substrates the likelihood of encountering angles greater than 54.7° for 0 is increased. Quantitative fits involving such resonances, especially those falling near the 54.7° angle are subject to large relative errors[24]. Therefore, we have chosen not to report quantitative fits of calculatedto-observed shifts. Qualitative analysis of the shifts we have observed can be made on the basis of model compound calculations, steric and other chemical characteristics of the compounds at hand, and the substantial correlations which have been made in the analysis of induced shifts in substrates of known stereochemistry[13]. The observed relative induced proton shifts for various monoesters are tabulated in Table 4. These shifts were obtained by regression analysis of the chemical shifts of a given proton onto those of a reference proton as a function of increasing LSR copcentration. The relative shift of the reference proton then assumes the value of 1.00 in the tables. Unless otherwise indicated, the induced shifts were obtained using Eu(fod)3. No

significant contact shift was observed with Gd(fod)3, which, because of its isotropic shift, can only contribute contact shift. Diamagnetic shifts were examined using La(fod)3 and found to be quite small at levels of doping employed in this study. Relative shifts reported in Table 4 are uncorrected for diamagnetic shifts. Positive values of relative shifts indicate proton resonances which moved downfield from TMS which is the usual displacement observed with Eu(fod)3 or Yb(fod)3 (i.e. when angles of 0 are less than 54.7°, eqn (2)). Negative values indicate resonances moving toward TMS. Qualitatively, we propose that the LSR is coordinating independently at both osmyl oxygens in the Os monoester in a roughly collinear fashion with the osmyl group, Fig. 1. Thus, the bpy ligand and the ester oxygens lie approximately in a plane perpendicular to the osmyl axis. For example consider the Os bpy monoester of p-pinene. The shifts of the bpy ligand indicate that the two ortho protons (Nos. 28, 35) are shifted relatively rapidly in the normal direction downfield from TMS. Assuming an effectively axially symmetric case (first term of eqn (2)), we reason that 0 angles involving the ortho protons must be less than 54.7°. At angles near 54.70 shifts are expected to be of small absolute magnitude. The interior protons of bpy exhibit small positive or negative relative shifts indicating that they fall very close to the cone of angles at 54.70. An examination of molecular models approximating expected stereochemistry and calculations from such models bear out this reasoning at lanthanide-osmyl oxygen association distances of about 2.0 A. Coordination at the ester oxygens is not expected to be as sterically favored nor are the observed shifts as consistent with these association sites. In a parallel study, we find qualitatively that Yb(fod)3 coordinates in roughly the same manner as Eu(fod)3 with B-pinene monoester, but at somewhat longer coordination distances from the osmyl oxygens. The Yb complex therefore induces positive shifts in all bpy resonances. Upon replacement of bpy with the DDphen ligand, the benzene rings of the ligand are expected to be moved into the higher angle region based on the association model given above for Eu(fod)3 interacting with the Os bpy monoester of/3-pinene. The protons of the benzene rings (all ten protons appear as a slightly broadened singlet) are expected and observed to have larger negative relative shifts than the protons of bpy. When two pyridine rings replace the bpy ligand, they are sterically constrained to assume positions approximately parallel to the osmyl group axis. However,

Spectroscopic properties of Os(Vl) monoesters containing heterocyclic nitrogen ligands Table 4. Observed relative shifts for Os monoesters by alkene, ligand* PROTON #

B-plnene, bp~

B-plnene, bpy [ ~ ( f o d ) ~ ]

B-plnene, DDphen

B-plnene, bispy

28

1.15

1.16

1.00

1.00

29

-.029

0.222

-.090

-.021

30

-.099

0.157

-.124

-.067

31

-.077

0.407

-.221

-.021

32

-.077

0.407

-.221

-.02t

33

-.099

0.157

-.124

-.067

34

-.029

0.045

0.013

-.021

35

1.00

1.00

1.60

1.00

36

0.515

0.635

0.155

37

0.347

40

0,047

0.027

0.070

0.010

41

0.102

0.054

0.195

0.010

-

0.479

44 45

0.490

46

0.724

0.653

1.45

0.373

47

0,701

0.653

1.38

0.391

48

-

1.00

49

-

1.00

a-pinene, ~y

PROTON#

cis-3-methyl-2pentene, bpy

28

1.00

24

0.603

29

-.147

25

-.009

30

-.121

26

-.048

31

0.122

27

-.030

32

0.122

28

-.067

33

-.050

29

-.I00

PROTON#

34

-.147

30

-.041

35

1.60

31

1.00

36

1.70

32

0.628

38

0.487

33

0,368

41

1.38

36

0.244

43

0.272

37

0.137

44

0.158

45

0.624

PROTON #

cis-4-methyl2-pentene, bpy

trans-4-methyl2-pentene, bgy

cis-2-octene, bp[

trans-2octene, bp[

21

1.00

1.78

1.00

1.00

22

-.050

-,032

-.026

-.004

23

-.112

-,026

-.0~3

-.081

24

-.050

-.117

-.040

-.073

25

-.084

-.200

-.040

-.074

12813

1284

W.C. BRUMLEY and C. C. HINCKLEY Table 4. (Contd)

PROTON #

cis-4-methyl2-pentene, bpy

trans-4-methyl2-pentene, bpy

cis-2-octene, bpy

t rans-2octene, bp~

26

-.144

-.186

-.083

-. 102

27

-.108

-.028

-.026

-.018

28

1.24

1.00

0.962

I. ii

29

I. 06

I. 34

0.815

0.821

30

1.06

0.983

0.815

0.877

31

0.634

0.533

0.397

0.292

34

0.122

0.120

35

0.180

0.184

*LSR is Eu(fod) 3 unless otherwise

indicated.

the protons of the bispy ligands are shifted in a manner similar to the bpy protons as they fall in analogous angular regions for the same coordination geometry. Whether the ligand is bpy, bispy, or DDphen, the observed relative shifts of /3-pinene such as those involving the methylene protons (Nos. 46, 47) and bridgehead methyl groups (Nos. 40,41) are consistent with osmyl oxygen association sites rather than ester oxygen sites. However, from a strictly qualitative analysis, the LSR data are consistent with Os ester attachment on either the near or far side relative to the bridgehead methyl groups in/3-pinene and a-pinene. The proposed structures appear to be the most likely, sterically, from an examination of molecular models and are the most consistent with calculations based on molecular models with the caveat of the limitations discussed above. Induced shifts for the monoesters derived from acyclic alkenes similarly provide indices for their identification. The monoesters derived from cis/trans isomers exhibit similar but unique shifted spectra. Distinction of cis/trans isomerism in the native alkene by use of Os bpy monoesters and LSR shifts does not appear qualitatively possible. CONCLUSION The formation of Os monoesters in the presence of heterocyclic nitrogen donors according to eqn (1) appears to lead to a unique stereochemical compound. This finding is based on NMR studies using an LSR and IR and UV-visible spectra. The relative induced shifts provide indices for the identification of these compounds. The finding of one product places limitations upon the mechanistic hypotheses concerning reaction (1). The formation of both osmium ester oxygen bonds to the alkene must occur together rather than as a discrete two step addition. A two step addition would allow rotation about the pertinent carbon--carbon bond to occur between steps and thereby lead to two products. A cyclic transition state arising from a concerted attack at the double bond is one possible hypothesis consistent with a one product reaction path. Acknowledgements--This research was supported in part with a grant from the National Science Foundation, by Southern Illinois University in the form of an assistantship (WCB) and computer time, and by the A. P. Sloan Foundation (CCH, Sloan Fellow 1973-1975). REFERENCES

1. R. Criegee, Ann 522, 75 (1936).

2. R. Criegee, B. Marchand and H. Wannowius, Ann 550, 99 (1942). 3. L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, pp. 75%764. Wiley, New York (1967). 4. R. Collin, W. P. Gritfith, F. L. Phillips and A. C. Skapski, Biochim Biophys Acta 320, 745 (1973) and Refs. therein. 5. C. C. Hinckley and J. A. Murphy, J. Histochem Cytochem 23, 123 (1975). 6. L. R. Subbaraman, J. Subbaraman, J. Subbaraman and E. J. Behrman, J. Organometal. Chem. 38, 1499 (1973) and earlier Refs. 7. A.J. Nielson and W. P. Griffith,J. Chem. Soc., Dalton Trans. 1501 (1978). 8. M. Schroeder and W. P. Griflith, J. Chem. Soc., Dalton Trans. 1599(1978). 9. J. F. Conn, J. J. Kim, F. L. Suddath, P. Blattman and A. Rich, J. Am. Chem. Soc. 96, 7152 (1974). 10. W. P. Griflith, The Chemistry of the Rarer Platinum Metals (Os, Ru, Ir and Rh). Wiley-lnterscience, New York (1967). 11. R. J. Collin, J. Jones and W. P. Grilfith,J. Chem. Soc., Dalton Trans. 1094(1974). 12. L. G. Marzilli, B. E. Hanson, T. J. Kistenmacher, L. A. Epps and R. C. Stewart, lnorg. Chem. 15, 1661 (1976). 13. R. E. Sievers [Ed.], Nuclear Magnetic Resonance Shift Reagents. Academic Press, New York (1973). 14. J. W. Emsley, J. Feeney and L. H. Sutcliffe, High Resolution Nuclear Magnetic Resonance Spectroscopy, Vol. L Pergamon Press, Oxford (1%5). 15. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 3rd Edn., pp. 1061-1062.Wiley-Interscience,New York (1972). 16. W. P. Griffith,J. Chem. Soc. 244 (1964). 17. W. P. Gritfith and R. Rose,i, J. Chem. Soc., Dalton Trans. 1449 (1972). 18. J. S. Strukl and J. L. Waiter, Spectrochim Acta 27A, 223 (1971). 19. K. Nakamoto, IR Spectra of Inorganic and Coordination Compounds, 2nd Edn. Wiley-Interscience, New York (1970). 20. W. C. Brumley, Structure Studies of the Organic Esters of Osmium(Vl) Using Lanthanide Shift Reagents, Dissertation, Southern Illinois University, 1975. 21. Edited by A. F. Trotman-Dickenson, Vol. 3, p. 732. Comprehensive Inorganic Chemistry, Pergamon Press, Oxford (1973). 22. Edited by A. F. Trotman-Dickenson,Vol. 5, p. 300. Comprehensive Inorganic Chemistry, Pergamon Press, Oxford (1973). 23. C. C. Hinckley and W. C. Brumley, J. Magn. Resonance 24, 239 (1976). 24. R. E. Cramer and R. B. Maynard, J. Magn. Resonance 31, 295 (1978). 25. D. J. Raber, M. D. Johnston, Jr., C. M. Campbell, C. M. Janks and P. Sutton, Org. Magn. Resonance 11, 323 (1978). 26. R. E. Lenkinski, G. A. Elgavish and J. Reuben, Z Magn. Resonance 32, 367 (1978).