Organometallics 1995, 14, 3264-3267
3264
Synthesis and Characterization of the @-Bonded, Quasi-Linear,Metal(I1) Diaryls MMes*z (M = Mg, Mn, Fe; Mes* = 2,4,6-t-Bu3CsHz-) Rudolf J. Wehmschulte and Philip P. Power* Department of Chemistry, University of California, Davis, California 95616 Received March 10,1995@ Disproportionation of a THF solution of Mes*MgBr (Mes* = 2,4,6-t-Bu&sHz) with 1,4dioxane affords MgMes*z (1). The treatment of activated MnC12 or FeBr2 with MgMes*2 in ether, and in the presence of l,bdioxane, affords the manganese(I1) and iron(I1) diaryls MnMes*2 (2) and FeMes*2 (3)as thermally stable pale yellow or yellow crystals in moderate yield, The X-ray crystal structures of 1-3 feature rare examples of two-coordinate metal(11)diaryls. The Mg-C, Mn-C, and Fe-C distances are 2.116(3), 2.108(2), and 2.058(4) respectively, and the C-M-C angles are in the range 157.9(2)-159.66(10)". There are also close (ea. 2.2-2.3 A) contacts involving the metal and hydrogens from the ortho-t-Bu groups. No reactions were observed between MMes*2 and THF, pyridine, or acetonitrile. Crystal data a t 130 K with Mo Ka (1 = 0.710 73 (2 and 3) or Cu K a (1 = 1.541 78 (1) radiation: C36H58Mg(l),M , = 515.13, a = 9.823(2) b = 15.511(8) c = 22.501(4) a = 96.88(3)", ,!? = 97.85(2)", y = 98.77(3)", triclinic, space grou P1, 2 = 4, R = 0.059 for 6304 ( I > 241)) data; C36H58Mn (2), M , = 545.76, u = 17.705(10) b = 8.576(4) C = 23.252(11) ,!? = 108.51(4)", monoclinic, space group C2/c, 2 = 4, R = 0.047 for 3133 (I > 241)) data; C36H58Fe (31,M , = 546.67, a = 17.763(12) b = 8.593(4) c = 23.365(13) ,!? = 109.49(4)", monoclinic, space group C2/c, 2 = 4, R = 0.067 for 2740 ( I > 241)) data.
A,
A)
A,
1,
A,
A,
A) A,
A,
A,
A, A,
Introduction
Experimental Section
Well-characterized, two-coordinate, open-shell (i.e. d0-d9), transition metal organometallic species are confined t o the three manganese dialkyls Mn{CHdtB u ) } ~Mn{CH(SiMe3)2}2,2 ,~ and Mn{C(SiMe3)3}2.3 The X-ray crystal structure of the latter shows that it is a linear monomer in the solid.3 Electron diffraction studies of Mn{CH&-Bu)}2l and Mn{cH(SiMe3)~)2~ demonstrate that they are linear and monomeric in the vapor, but there is evidence that indicates that they are associated in the condensed p h a ~ e . In ~ . this ~ paper the synthesis and characterization of the new monomeric, two-coordinate, d5 and d6 manganese(I1) and iron(I1) diaryls, MnMes*2(2) and FeMes"2 (3)5(Mes* = 2,4,6-tBu&&-), are reported. They were synthesized by the addition of the novel magnesium diary1 MgMes*2 (1) with the appropriate metal dihalides. The monomeric diorganomagnesium species 1,which has a two-coordinate Mg(I1) center in the crystal phase, is only precedented in the literature by the crystal structure of Mg{C(SiMe3)3h6
General Procedures. All work was performed under anaerobic and anhydrous conditions by using Schlenk techniques or a Vacuum Atmospheres HE-43-2 drybox. Solvents were distilled from sodiudpotassium alloy and degassed twice prior to use. Physical Measurements. lH NMR and l3C NMR spectra were obtained on a General Electric QE-300 spectrometer using either CsDs or C,DB solvent. Magnetic measurements were performed with a Johnson-Mathey magnetic balance. W-visible spectra were obtained on a Hitachi U-2000 spectrophotometer. Starting Materials. Magnesium turnings and FeBrz were purchased from commercial suppliers and used as received. Activated MnC12, and Mes'"B1.8 were synthesized by literature procedures. Synthesis of MgMeskz(1). Magnesium turnings (0.04 g, 16.4 mmol) were activated by grinding with a mortar and pestle followed by a 1-2 h of stirring under reduced pressure at ca. 60 "C. They were then treated with 50-100 pL of BrCHzCHzBr in THF (20 mL) at reflux temperature. After 30 min Mes'%Br(5.35 g, 16.4 mmol) in THF (100 mL) was added dropwise. Continued refluxing for 3 h resulted in almost complete consumption of the magnesium. The Grignard solution was then treated with 1,4-dioxane (0.73 g, 8.2 mmol) and refluxed for 24 h. The volatile components were removed under reduced pressure, and the resultant colorless solid was then extracted with 2 x 60 mL of n-hexane to give a cloudy solution. Filtration and reduction of the volume to ca. 30 mL, followed by storage for several days in a -20 "C freezer, afforded the product MgMes'"2 as colorless crystals. Yield:
Abstract published in Advance ACS Abstracts, June 1, 1995. (1)Andersen, R. A,; Haaland, A,; Rypdal, R;Volden, H. V. J . Chem. SOC.,Chem. Commun. 1985,1807.
(2i Andersen, R. A.; Berg, D. J.; Fernhold, L.; Faegri, K.; Green, J . C.; Haaland, A.; Lappert, M. F.; Leung, W.-P.; Rypdal, K. Acta Chem. Scand. 1988,42A, 554. t3)Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith, J. D.; Sullivan, A. C. J . Chem. SOC.,Chem. Commun. 1985, 1380. 14) Andersen, R. A.; Carmona-Guzman, E.; Gibson, J. F.; Wilkinson, Dalton Trans. 1976, 2204. G. J . Chem. SOC., 15) After this work had been submitted, we became aware that a very recent report also disclosed the synthesis and structure of FeMes'", which was made by the treatment of FeBm(THF)*with the Grignard reagent. It is apparent from a comparison of the data for this compound and 3 that they are identical: Mtiller, H.; Seidel, W.; Gorls, H. Angew. Chem., Int. Ed. Engl. 1995, 36, 325.
( 6 )A-Juaid, S. S.; Eaborn, C.; Hitchcock, P. B.; McGeary, C. A.; Smith, J. D. J . Chem. SOC., Chem. Commun. 1989, 273. ( 7 )Horvath, B.; Moseler, R.; Horvath, E. G. Z.Anorg. Allg. Chem. 1979, 450, 165. 18) Pearson, D. E.; Frazer, M. G.; Frazer, V. S.; Washburn, C. L. Synthesis 1976, 621.
0276-733319512314-3264$09.00100 1995 American Chemical Society
Quasi-Linear MetaKII) Diaryls
Organometallics, Vol. 14, No. 7, 1995 3265
Table 1. Selected Crystallographic Data for 1-3= ~~
2
1
formula fw c q t syst
G&d%'
515.13 triclinic a,A 9.823(2) b, A 15.571(8) c, A 22.501(41 a, deg 96.88(31 /A deg 97.85(2) 7, deg 98.77(3) v, A3 33_35(2) spacegroup P1 Z 4 deale,g ~ m - ~ 1.026 I(,"-' 0.586 20 range, deg 0-114 no. of obsd d n s 6304 (I> 2 d ) ) no. of variables 761 R , Rwb 0.05910. 145
~
~~
3
C ~ ~ H S E M ~ C:jSHssFe 545.76 17.705(10) 8.576(4) 23.252(11)
546.67 monoclinic 17.763(12) 8.593(4) 23.365( 13)
108.51(4)
109.49(4)
3348(3) C2le 4 1.083 0.415 0-55 3133 (I> 2rrtI)) 227 0.04710.111
3362(3) C2le 4 1.080 0.469 0-55 2740 (I> 2rHZ)) 208 0.06710.164
monoclinic
Data were collected at 130 K with Mo Ka (1 = 0.710 73 A)(2 and 3) or Cu Ka (1= 1.541 78 A)(1)radiation. Based on FO' and F2values. 1.85 g, 44%. Mp: softens at 200 "C, turns red at 250 "C. 'H NMR (C&): 7.57 (s,m-H, 4H), 1.48 (s,O-CH3, 36H), 1.43 (s, p-CH3, 18H). 13C{1H]NMR (C&): 159.3 (o-C), 148.2 (p-C), 146.3 (i-C),119.6 (m-C),38.2 (o-CXCH~)~), 34.9 (p-C(CHs)3),34.0 (O-CH3), 31.9 (p-CH3). MnMes*2 (2). A slurry of 0.31 g (2.5 mmol) of activated MnC1z7in 30 mL of THF and 0.5 mL (5.9 mmol) of 1,4-dioxane was treated dropwise with a solution of 1.29 g (2.5 mmol) of MgMeszk2in Et20 (30 mL) at -20 "C. After 1 h at -20 "C, and slow warming to room temperature, the resultant clear pale yellow solution was stirred for another 22 h during which time the solution became cloudy. The volatile components were removed, and the resulting solid was extracted with 100 mL of n-hexane. Concentration of the hexane solution to 1015 mL followed by cooling in a -20 "C freezer leads to the isolation of 0.25 g of MnMesZh2 in the form of large (2-5 mm) pale yellow air-sensitive crystals. Yield: 18%. Mp: 205-210 "C (melts and turns black). per = 5.90(0.1) jig. W/vis (benzene): no absorption 400-1100 nm. IH NMR (ca. 15 mg in 0.3 mL of C,&): 8.3 (s, broad, Av1/2 = 270 Hz). An additional broad, weak signal at 48 ppm with v112 2000 Hz could not be well resolved due to phasing problems. FeMes*2 (3). A 0.65 g (3.0 mmol) amount of FeBrn was added via solid addition funnel to a solution of MgMes'Ea(1.58 g, 3.07 mmol) in Et20 (80 mL) at 0 "C. The mixture was slowly warmed to room temperature and stirred for 16 h. To the pale yellow solution, which still contained unreacted FeBrn (brownish solid), was added 1,4-dioxane (0.34 mL, 4.0 mmol, 0.35 g), and the resulting yellow green mixture was heated to reflux for 3 h. Filtration of the bright yellow solution, concentration under reduced pressure to ca. 5 mL, and crystallization in a -20 "C freezer for 1 week leads to the formation of yellow, extremely air-sensitive, X-ray-quality crystals. Yield: 0.72 g (43.9%). Mp: darkens at 185 "C, melts with decomposition at 193-195 "C (turns black). per = 5.1N0.1) p g . W/vis: intense absorption (log 6 > lo4)between 400 and 200 nm with a shoulder at 460 nm. 'H NMR (CsD6,22 "C, 40 mg in ca. 0.4 mL, 300 MHz): 121.0 (s, br, Avliz = 680 Hz, m-H, 4H), 61.0 (s, br, A v l ~= 2600 Hz, o-CH3, 36H), 26.2 (s, A v ~ 2= 270 Hz, p-CH3, 18H). X-ray Crystallographic Studies. The X-ray data were collected on a Siemens R3mN (2, 3) or a Syntex P21 (1) diffractometer equipped with a locally modified Enraf-Nonius LT device. The data were collected by using graphite-monochromated Mo Ka (i = 0.710 73 A) ( 2 and 3) or Cu Ka (A = 1.541 78 A) (1)radiation. Calculations were those of SHELXTL94 installed on an IBM 386 PC. Scattering factors were 2
obtained from ref 9. An absorption correction was applied by using the method described in ref 10. All structures were solved by direct methods and Fourier difference maps. They were refined by full-matrix least-squares procedures. All nonhydrogen atoms were refined anisotropically at calculated positions using a riding model with the parameters given in SHELXTL-94. The structures showed disorder either in a para-t-Bu group ( 1 and 3)or in ortho and para-t-Bu groups (2). These were refined successfully with split occupancies. Some details of the crystallographic data are given in Table 1, coordinates for important atoms are given in Table 2, and selected bond distances and angles are provided in Table 3.
Results and Discussion Syntheses. The compound MgMes*z was synthesized by the addition of 1,Cdioxane to the Grignard reagent Mes*MgBr (eq 1). The isolation of 1 as an 2Mes*MgBr
+ 2 1,6dioxane MgMes*, 1
+ MgBr,(l,bdioxane),
(1)
uncomplexed species from THF solution is remarkable since diorganomagnesiumcompounds normally complex strongly with two donor molecules to give a distorted tetrahedral coordination a t the magnesium.ll The compound 1 smoothly converts MnClz or FeBrz to MnMes*2 (2) or FeMes*z (3)by stirring in ether at room temperature in the presence of 2 equiv of 1,Cdioxane (eqs 2 or 3). The use of 1,4-dioxane helps to drive the MgMes*,
+ MnC1, -
+
M ~ M ~ S MgCl,(l,Cdioxane), * ~ (2) ( I
Y
MgMes*,
+ FeBr, -
FeMes*,
+ MgBr,(l,Cdioxane),
(3)
3 reaction to completion by precipitating the magnesium halide as a 1,Cdioxane complex. Similar experiments involving the treatment of MgMes*z with VBr2, CrC12, or CoC12 have not yet afforded stable diary1 derivatives of V, Cr, or Co. Structures. The structures of 1 (Figure 1 ) , 2(Figure 21, and 3 (Table of Contents illustration) are very similar, and in fact, the crystals of 2 and 3 are isomorphous. The close relationship between the three structures is evident from the data in Table 3. The basic structural motif consists of a two-coordinate metal bound t o two Mes* groups (with a crystallographically required 2-fold axis, which bisects the C-M-C angle, in the case of 2 and 3). There are further secondary interactions between the metals and ortho-t-Bu hydrogens as listed in Table 3. The M-C bond lengths vary only slightly, and the Mg-C and Mn-C distances are within three standard deviations of each other. The Fe-C distance is slightly shorter, having a value of 2.058(4) A,which is in keeping with the smaller size of the Fez+ion. Each compound has a bent geometry with C-M-C angles in the narrow range 157.9(2)( 9 )International Tables for X-Ray Crystallography; D. Reidel Publishing Co.: Dordrecht, The Netherlands, 1993; Vol. C. f 10)Parkin, S. R.; Moezzi, B.; Hope, H. J . Appl. Crystallogr. 1995, 28, 53. (11)Markie, P. R.; Akkerman, 0. S.; Bickelhaupt, F.; Smeets, W. J. J.;Spek, A. L. A d v . Organomet. Chem. 1991, 37. 47.
Wehmschulte and Power
3266 Organometallics, Vol. 14, No. 7, 1995
Table 2. Atomic Coordinates ( x lo4)for 1," 2, and 3 Y
X
z
Y
X
2
Compound 1 3846( 1) 4405(3) 3428(3) 3857(3) 5252(3) 62 12(3) 5818(3) 1830(3) 1173(3) 1410(3) 120%3) 5672(3) 5042(4) 5139(4) 7252(3) 775x3) 7755(3) 8075(3) 6548(3) 2834(3) 2515(3)
1299(1) 577(2) -83(2) -722(2) -751(2) -87(2) 566(2) -133(2) -1013(2) 599(2) -60(2) -1462(2) -2369(2) -1350(2) -1411(2) 1743(2) 1743(2) 872(2) 1990(2) 1550(2) 907(2)
1533(3) 1533(3) 828(3) 1176(3) 2 147(3) 3220(3) 429714) 2112(3) 3968(3) -242(3) -1334(5) -1005(5) 527(5) -523(12) 257(12) 257(12) 2431(3) 1092(3) 354x31 2690(3 1
983(2) 983(2) 1690(2) 2339(2) 2283(2) 84(2) 43(2) -747(2) 82(2) 1760(2) 942(3) 2552(3) 1895(3) 900(7) 2499(7) 2499(7) 3083(2) 3187(2) 3017(2) 3912(2)
9047( 1) 9047(1) 9096(1) 8747(1) 8351(1) 8673(1) 8255(2 8484(2) 9318( 1) 9530( 1) 9406(2) 9451(2) 10182(2) 9847(5) 10013(5) 10013(5) 8015(1) 7609( 1) 7610(2) 8483( 1)
5000 6011(1) 675U 1) 7464( 1) 749U 1) 6765( 1) 6039( 1) 6840( 1) 7367(1) 7209(1) 6051(1) 8283( 1) 8286(3)
2512( 1) 2078(2) 2804(2) 2211(2) 912(2) 240(2) 799(2) 4307(2) 4015(3) 5582(3) 4974(3) 282(2) 570(6)
90 14(2) 8354(3) 8674(3) 8829(3) 8198(3 5284(1) 45 12(2) 5286(2) 5314(2) 4680(2) 5372(4) 4902(3)
1170(6) -1377(5) 1456(6) -186(7) - 1284(6) -32(2) 673(4) 90(5) -1741(3) 1124(3 -1256(3) - 1047(3)
4422(2) 4382(2) 4956(2) 4103(2) 48 16(2) 3695(1) 3295(2) 4349(1) 3527(1) 3797(3) 4217( 1) 3106( 1)
2528(1) 2068(4) 2781(4) 2187(4) 898(4) 235(4) 792(4) 4269(4) 3933(5) 5555(5) 4945(5)
8270(2) 8288(6) 9008(5) 8354(5) 8661(6) 8798(6) 8173(6) 5261(2) 4486(3) 5249(3) 5287(3)
26.55) 583(13) 1153(12) - 1384(11) 1443(12) -207(14) - 1278(11) -51(4) 667(7) 43(7) - 1758(6)
4505(2) 5158(4) 4436(5) 4390(4) 4966(56) 4132(4) 4837(5) 3679(2) 3728(2) 4326(2) 3504(2)
5000 5986(2) 6731(2) 7449(2) 7472(2) 6749(2) 6015(2) 6818(2) 7323(2) 7217(2) 6021(2) a
Data for only one molecule in the asymmetric unit are given.
Table 3. Selected Bbnd Distances (A>and Angles (deal for 1-3 M-C
C-M-C H- - -M C- - -M torsion angle CzM-Ar torsion angle Ar-Ar angle between M-C and vector C(ipso)-C(parai
158.35(10) 158.03(10) 2.28 (H18A) 2.28 (H70B) 2.72 (C35) 2.71 (C53) 46.7 (Cl-C6) 43.8 (C19-C24) 45.0 (C37-C42) 48.0 (C55-C60) 73.3 75.0 15.9 (CI-C4i 14.7 (C19-C22i 15.4 (C37-C40) 16.1 (C55-C58)
159.66(10)
157.9(2)
2.27 (HlOB)
2.18 (HlOB) 2.29 (H16C) 2.23 (H16C) 2.78 ((216) 2.73 (C10)
W 45.8
46.4
74.5
75.5
15.6
15.1
159.66(10)". The angles between the perpendiculars to the aromatic ring planes when viewed along an M-C
Figure 1. Thermal ellipsoidal plot of one of the molecules in the asymmetric unit of 1. Hydrogen atoms are not
shown for clarity. Important bond distances and angles are given in Table 3. bond vary from 73.3 to 75.5'. Some steric strain is also suggested by the fact that all the ring planes (exemplified by the C(ipso)-C(para) vector) are bent by ca. 15" from the line of the M-C(ipso) bond. Discussion. The compounds 1-3 represent very rare examples of structurally authenticated two-coor-
Quasi-Linear Metal(II) Diaryls
W
Figure 2. Thermal ellipsoidal plot of one of 2. Hydrogen atoms are not shown for clarity. Important bond distances and angles are given in Table 3.
dinate Mg, Mn, or Fe centers in the solid state.12 The low coordination is a consequence of the large steric requirements of the Mes* group. In the case of magnesium, the crystal structures of two-coordinate species are Mg{C(SiMe3)3}z6(4) and Mg{N(SiMePhzh}z14 (5). The compound 4 has a linear geometry and an Mg-C distance of 2.166(2) 8, which is slightly longer than that observed in 1. Interestingly, the amido complex 5 has an interligand angle of 162.8(3)"which is close to that measured for 1. MgMes*z does not form stable complexes with THF or EtzO, and this behavior may be contrasted with the bis(tetrahydr0furan) complexes formed by Mg(2,4,6-R3CsHz)z(R = Me or i-Pr).15 The structure of the manganese species 2 is precedented by those of the alkyl derivatives mentioned in the Introduction. Only the two-coordinate derivative Mn{C(SiMe3)3}~ (linear geometry)has been structurally characterized in the solid state,3 however, and the Mn-C distance 2.101(4)A is practically identical to the 2.109(2)A found for 2. The steric effect of the large size of the Mes* ligand in MnMes*z may be contrasted with that of the Mes ligand, which results in the isolation of the trimer MesMn(p-Mes)zMn&-Mes)zMnMes.l6 Twocoordination at iron has precedent only in the solid state structures of the related amides and thiolates Fe{N(SiMePhz)z)2,l7J8 Fe{N(SiMe2Ph)z}~,'~ Fe(NM e s B M e s z ) ~F, ~~~{ N ( S ~ M ~ ~ ) Zand } S Fe(SR)zZ0 R , ~ ~ (R = 2,6-MeszCsH3-) and in the vapor-phase structure of Fe{N(SiMe3)~}2.~'These molecules feature interligand angles at iron that vary from ca. 120" in the thiolate derivatives t o 180" in Fe(N(SiMe&)z. The Fe-C distance in 1, 2.058(4) A, is significantly longer than the Fe-N distances in Fe(N(SiMe2Ph)z)~'~ (1.903(7)A)
Organometallics, Vol. 14, No. 7, 1995 3267
or F ~ { N ( S ~ M ~ P ~ Z(1.917(2) ) Z } Z ~A). ~ J ~The difference in metal-ligand bond lengths (ca. 0.14-0.15 A), which is much greater than the difference between the radii of carbon (0.77 A) and nitrogen (0.73 A), can be attributed in part to the greater ionic character of the Fe-N bond. The quasi-linear structures observed for 2 and 3 suggest high spin d5-or d6-electron configurations. This is confirmed by magnetic moments of 5.90(0.1) and 5.18(0.1) p g at 25 "C, which are consistent with the presence of five and four unpaired electrons, respectively. The 'H NMR spectrum of 2 displays a broad singlet a t 8.3 ppm and a further, much broader, signal at 48 ppm. The 'H NMR spectrum of 3, however, displays three assignable paramagnetically s e d peaks at 6 = 121.0 (m-HI, 61.0 (o-C(CH&, and 26.2 (pC(CH3)3)in C6D6 at 25 "c. The uv-vis spectrum of 3 in hexane displayed a rise in absorption toward higher energy with a shoulder observed at 460 nm, whereas the corresponding spectrum of 2 was essentially featureless between 400 and 1100 nm. Unlike M(N(SiMe&}z (M = Mn or Fe), which are dimers in the solid22~23 and form complexes with THFZ2 or pyridine,24 neither MnMes*z nor FeMes*z forms complexes with THF, pyridine, or acetonitrile. It therefore appears that the MMes*z molecules are quite sterically encumbered and much more hindered than the less crowded dimeric, diary1 analogues such as (MnMes2)3,16( F e M e s z ) ~and , ~ ~(FeTripz)zZ6(Mes = 2,4,6Me3CsHz and Trip = 2,4,6-i-PrsC6Hz). The similar bending in 1-3 is probably due to weak interactions between ortho C-H groups and the metal orbitals. This may be contrasted with the almost linear structure observed (C-Hg-C 173.4(2)", Hg-C = 2.080(6) A) for H g M e s * ~ .The ~ ~ compounds 1-3 are stable for several weeks when stored in a nitrogen atmosphere. The chromium(I1) (d4)and a cobalt(I1) (d7)analogues of 2 and 3 are significantly less stable and apparently decompose under ambient conditions.28 The properties of these and reactivity studies of 1-3 will be described in a future publication. Acknowledgment. We thank the National Science Foundation and the donors of the Petroleum Research Fund, administered by the American Chemical Society, for financial support.
Supporting Information Available: Tables of data collection parameters, complete atom coordinates and U values, (12) Power, P. P. Comments Inorg. Chem. 1989,8,177; Chemtracts: bond distances and angles, and anisotropic thermal paramInorg. Chem., in press. (13) It could be argued that the species [Mg{CH(SiMe3)*}{CH(SiMe3)- eters, and ORTEP diagrams (34pages). Ordering information SiMez-p-Me}], has a two-coordinate Mg center. It has, however, been is given on any current masthead page.
described as associated with intermolecular agostic interactions. Moreover, the C-Mg-C angle is 140.0(2)": Hitchcock, P. B.; Howard, J. A. K.; Lappert, M. F.; Leung, W. P.; Mason, S. A. J. Chem. Soc., Chem. Commun. 1990, 847. (14) Bartlett, R. A.: Olmstead, M. M.; Power, P. P. Inorp. - Chem. 1994, 33, 4800. (15) Waggoner, IC; Power, P. P. Organometallics 1992, 11, 3209. (16) Gambarotta, S.; Floriani. C.: Chiesi-Villa. A.: Guastini. C. J. Chem. Soc., Chem. Commun. 1983, 1128. (17) Bartlett, R. A.; Power, P. P. J.Am. Chem. Soc. 1987,109,7563.
(18)Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M. M.; Power. P. P. J. Am. Chem. Soc. 1989.111.4338. ~~~. ~~~(19) Chen, H.; Bartlett, RTA.; Olmstead, M. M.; Power, P. P. J.Am. Chem. SOC.1990,112, 1048. (20) Ellison, J. J.; Ruhlandt-Senge, K.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1994, 33, 1178. (21) Andersen, R. A.; Faegri, K.; Green, J. C.; Haaland, A,; Lappert, M. F.; Leung, W.-P.; Rypdal, K. Inorg. Chem. 1988, 27, 1782. I
OM950268C (22) (a)Bradley, D. C.; Hursthouse, M. B.; Malik, K. M. A.; Maseler, R. Transition Met. Chem. IWeinheim, Ger., 1978,3, 253. (b) Murray, B. D.; Power, P. P. Inorg. Chem. 1084,23, 4584. (23) Olmstead, M. M.; Power, P. P.; Shoner, S. C. Inorg. Chem. 1991, 30, 2547.
(24)Olmstead, M. M.; Power, P. P.; Shoner, S. C. Unpublished results. (25) ( a )Machelett, B. 2.Chem. 1976,16, 116. (b)Miiller, H.; Seidel, W.; Garls, H. J. Organomet. Chem. 1993, 445, 133. (26) Klose, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N. J. Am. Chem. SOC.1994,116, 9123. (27) Huffman, J. C.; Nugent, W. A,; Kochi, J. K Inorg. Chem. 1980, 19, 2749. (28) Wehmschulte, R. J.; Power, P. P. Unpublished results.
