Organometallics 1995,14,456-460
456
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Oxygen-Atom Transfer from Nitrous Oxide to an Organonickel(I1) Phosphine Complex. Syntheses and Reactions of New Nickel(I1)Aryloxides and the Crystal
Structure of ( M ~ ~ P C H ~ C H ~ P M ~ ~ ) N ~ ( ~ = O - C & C & M ~ ~ C H ~ Kwangmo Koo,la Gregory L. H i l l h o u s e , * J a and Arnold L. Rheingold*Jb Searle Chemistry Laboratory, Department of Chemistry, The University of Chicago, Chicago, Illinois 60637,and the Department of Chemistry, University of Delaware, Newark, Delaware 19716
- Received August 17, 1994@
I
Reaction of (PMe3)2Ni(CH2CMe2+,-CsH4)(1) with N2O gives the oxametallacycle [(PMea)Ni(OI
o-C6&CMe2CH2)]2 (2) and 0-PMe3.
I
Dimeric 2 reacts with CO to give the benzopyran CH2-
I
CMe2-o-C&OC(O) (3)and with HCl to give 2-tert-butylphenol. The chelating ligands 2,2'bipyridine (bipy), 1,lO-phenanthroline (phen), and 1,2-bis(dimethylphosphino)ethane(dmpe) react with 2 to afford the monomeric aryloxide complexes (bipy)Ni(O-o-CsH4CMe2CH2)(41,
(phen)Ni(O-o-C6H4CMe2CH2)(5),and (dmpe)Ni(O-o-CsH4CMe2CH2)(61, respectively. Reaction of 4 or 5 with CO affords good yields of the lactone 3. Treatment of 5 with I2 induces formal 0,C-reductive elimination, giving 4,4-dimethyl-3,4-dihydrocoumarin, d+,-Cs&CMez1
CH2 (9), in good yield. 6 has been characterized by single-crystal X-ray diffraction. 6 crystallizes from pentane solution in the monoclinic space group P2dn with a = 9.206(2) b = 12.685(3) c = 15.998(3) /3 = 90.33(3)", and 2 = 4. The least-squares refinement converged to R(F) = 4.04% and R(wF) = 4.89% for the 1989 unique data with F, > 4.5dFO).
A,
A,
A,
Introduction
1
We have been exploring the use of nitrous oxide as an 0-atom transfer reagent to organic ligands in transition-metal complexes. Our earlier studies concentrated on reactions of N20 with group 4 metallocene derivatives,2 especially alkyne complexes of Ti and Zr,3 but recently we have extended the scope of our research to include late-metal complexes, particularly those of square-planar nickel(I1)containing the n-acid coligands 2,2'-bipyridine (bipy) and 1,lO-phenanthroline hen).^ In these latter studies, interesting transformations were effected, notably the oxidation of simple alkyl groups attached to Ni t o give stable Ni alkoxides (eq 1). (L,)Ni-R
+ N,O - (LJNi-OR + N2
(1)
Is a z-acid bipyridine (or phenanthroline) an essential component in activating the (bipy)NiRa complexes toward reactivity with NzO? In addressing this question,
we have examined the reactivity of (PMe&k(CH2CMezAbstract published in Advance ACS Abstracts, December 1,1994. (1)(a) The University of Chicago. (b) University of Delaware. (2)Vaughan, G. A.; Rupert, P. B.; Hillhouse, G. L J. Am. Chem. SOC.1987,109, 5538. (3) (a) Vaughan, G. A.; Hillhouse, G. L.; Lum, R. T.; Buchwald, S. L.; Rheingold, A. L. J . Am. Chem. SOC.1988,110, 7215. (b) Vaughan, G. A.; Sofield, C. D.; Hillhouse, G. L.; Rheingold, A. L. J . Am. Chem. SOC. 1989,111, 5491. (c) Vaughan, G. A.; Hillhouse, G. L.; Rheingold, A. L. J . Am. Chem. SOC.1990, 112, 7994. (4) (a) Matsunaga, P. T.; Hillhouse, G. L.; Rheingold, A. L. J. Am. Chem. SOC.1993,115,2075. (b)Matsunaga, P. T.; Mavropoulos, J. C.; Hillhouse, G. L. Polyhedron 1994,13, in press.
o - C ~ H(~l I)5 with N2O and report herein the results of our study of this system.
Experimental Section General Considerations. Reactions were carried out using standard high-vacuum and Schlenk techniques using dry, air-free solvents. NMR spectra were recorded in CsDe or CD&lz solutions a t ambient temperature. lH NMR spectra were recorded a t 500 MHz using a General Electric Q-500 spectrometer; 13C{'H} NMR spectra were recorded using a GE 52-500or 52-300spectrometer operating at 125.00or 75.5MHz, respectively. 31P(1H}NMFt spectra were recorded using a GE 52-500operating a t 202.5MHz. Infrared spectra were recorded on a Nicolet 20SXB spectrometer in a Nujol mull with KBr plates. Electron impact mass spectra were recorded on a VG Analytical, LTD 70-70 EQ double focusing (EB)mass spectrometer. Elemental analyses were performed by Desert Analytics (Tucson, AZ). 2,2'-bipyridine (bipy) and 1 , l O phenanthroline (phen) were purchased from Aldrich Chemical Co., and 1,2-bis(dimethylphosphino)ethane (dmpe) was pur-
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chased from Strem Chemical Co. (PMes)zNi(CHzCMe29-CsH4) (1)was prepared according to literature method.6
@
Preparation of [(PMes)Ni(O-o-C~CMeaCH2)12 (2). A solution of 1(0.22g, 0.64"01) in benzene (10 mL) was stirred under an NzO atmosphere a t 55 "C for 3 d, the solution was filtered, and the filtrate was evaporated to dryness. The residue was extracted with 35 mL of n-hexane. The hexane solution was concentrated and cooled to -78 "C, to give 2 (0.10 (5) Carmona, E.; Palma, P.; Paneque, M.; Poveda, M. L.; G u t i h e z Puebla, E.; Monge, A. J . Am. Chem. SOC.1986,108, 6424.
0276-733319512314-0456$09.00/00 1995 American Chemical Society
Organometallics, Vol.14, No. 1, 1995 457
Syntheses and Reactions of New Nickel(II) Aryloxides g, 55%) as a yellow powder. lH NMR (C&): 6 7.56 (d, 2H, aryl), 7.26 (d, 2H, aryl), 7.11 (t, 2H, aryl), 6.85 (t, 2H, aryl), 1.58 (s,12H, CH3), 0.57 (m, 4H, CHZ),0.53 (d, 18H, PCH3, = 9 Hz). 31P{1H}NMR (CsD6): 6 -7.45. 13C{lH}NMR (c6D13, 125.7 MHz): 6 161.0, 140.2, 126.7, 125.3, 119.6, 117.7, 35.7, 31.0, 29.9 (d, 'Jpc = 29 Hz), 13.7 (d, ' J p c = 29 Hz). An analytical sample recrystallized from C&&exane was solvated with '/&H6. Anal. Calcd for CZgH45P202Niz: C, 57.6; H, 7.50. Found: C, 57.9; H, 7.62. Reaction of 2 with HCl. To a solution of 2 (0.37 g, 0.65 mmol) in benzene (10 mL) was introduced an excess of anhydrous HCl. The solution was stirred at ambient temperature for 10 min, the solution was filtered, and the filtrate was evaporated t o dryness using a rotary evaporator. The residue was dissolved in hexane and chromatographed on silica gel (eluent: hexane/ethyl acetate, 1:l)to give 2-tert-butylpheno1 (0.16 g, 81%). The product was identified by spectral comparison with an authentic sample. Preparation of 4,4-Dimethyl-2-oxo-Wll-benzopyran (3). A solution of 2 (0.20 g, 0.36 mmol) in benzene (10 mL) was stirred under a CO atmosphere at ambient temperature for 15 min, the solution was filtered, and the filtrate was evaporated t o dryness using a rotary evaporator. The residue was dissolved in hexane and chromatographed on silica gel (eluent: hexane/ethyl acetate, 1:l) to give 3 (0.04 g, 67%). IH NMR (CDZClz): 6 7.33 (d, lH, aryl), 7.25 (t, IH, aryl), 7.15 (t, l H , aryl), 7.03 (d, lH, aryl), 2.63 (s, 2H, CHz), 1.37 (9, 6H, CH3). 31C{1H} NMR (CD2C12, 125.7 MHz): 6 168.3 (C=O), 151.1 (aryl), 132.3 (aryl), 128.5 (aryl), 125.0 (aryl), 124.9 (aryl), 117.2 (aryl), 43.8 (CHz), 33.5 (CMeZ),27.7 (CH3). IR: v(C=O) 1775 (s) cm-l. EIMS m / z 176 (M+).
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Preparation of (bipy)Ni(O-o-C&CMe&Hd (4). To a cold solution of 2 (0.36 g, 0.66 mmol) in benzene (10 mL) was added 0.30 g of 2,Y-bipyridine (0.64 mmol). The reaction mixture was warmed to room temperature and stirred for 30 min, at which time the blue solution was filtered. The filtrate was dried in vacuo and washed with n-hexane (15 mL) to give crude 4 which was recrystallized from toluenehexane as blue needles (0.20 g, 43%). lH NMR (CsD6): 6 9.45-6.18 (m, 12H, aryl), 2.11 (s,2H, CHd, 1 . 9 2 ( ~6H, , CH3). l3C(lH} NMR(CdI6, 75.5 MHz): 6 148.2, 147.6, 136.4, 134.3, 126.5, 125.1, 120.6, 118.8,114.8, 40.9, 35.1, 31.4 (due to the low solubility of 4 in C&, two of its arylhipy resonances were not observed). Anal. Calcd for CzoHzoNzNiO: C, 66.2; H, 5.55; N, 7.71. Found: C, 66.0; H, 5.45; N, 7.51.
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Preparation of (phen)Ni(O-o-CsH4CMe2CH2)(5). Using a procedure analogous to that described above for 4, except that 1,lO-phenanthroline was used instead of 2,2'-bipyridine, reaction of 2 (0.15 g, 0.26 mmol) with phen (0.1 g, 0.52 mmol) yielded 5 (0.18 g, 88%)as dark purple-blue powder. lH NMR (CDC13): 6 9.42-6.4 (m, 12H, aryl), 2.00 (s,2H, CHd, 1.46 (s, 6H, CH3). Anal. Calcd for C2zH2oNzNiO: C, 68.3; H, 5.21; N, 7.24. Found: C, 68.8; H, 5.22; N, 6.70. The 13CNMR spectrum of 6 was not obtained due t o its low solubility in solvents with which it does not react over the time period needed to acquire carbon data. Preparation of (dmpe)Ni(O-o-CsH4CMe2CHa)(6). Using a procedure analogous to that described above for 4, except that 1,2-bis(dimethylphosphino)ethane was used instead of 2,2'-bipyridine, reaction of 2 (0.12 g, 0.21 mmol) with dmpe (70 pL, 0.42 mmol) yielded 6 (0.09 g, 60%) as yellow powder. lH NMR (C&): 6 7.57 (d, lH, aryl), 7.37 (t, l H , aryl), 7.29 (d, lH, aryl), 6.93 (t, l H , aryl), 1.82 (s,6H, CHd, 1.22 (m, 2H, CHz), 0.96 (d, 6H, PCH3, 2 J p = ~ 8 Hz), 0.75 (m, 2H, CHd, 0.71 = 8 Hz), 0.60 (m, 2H, CH2). 13C{lH}NMR (d, 6H, PCH3, 'JPH (C&, 125 MHz): 6 163.6, 138.2, 127.1, 125.2, 120.1, 114.2, 40.1 (dd, 'Jpc = 70 Hz, 'Jpc = 24 Hz), 35.1, 33.1 (d, 4 J ~ c= 7 = 25 Hz, l J p c = 70 Hz), 23.5 (dd, 2 J p (trans) ~ Hz), 30.1 (dd, = 25 Hz, 'Jpc (cis) = 11 Hz), 11.9 (d, 'Jpc = 29 Hz), 10.3 (d, ' J p c = 15 Hz). 31P(1H}N M R (CsDs): 6 35.1 (d, 'Jpp = 4 Hz),
Table 1. CrystallographicData for 6 formula formula weight crystal system space group a, A
b, 8, C, t J 3
A
deg
Crystal Parameters C16H28NiOP2 V, A3 357.0 2 monoclinic cryst dimens, mm F%/n cryst color 9.206(2) D(calc), g cm3 12.685(3) p(Mo Ka), cm-' 15.998(3) temp, K 90.33(3)
1868.1(6) 4 0.42 x 0.42 x 0.56 orange 1.269 12.04 297
Data Collection f i s collected diffractometer Siemens PI indpt fflns monochromator graphite Mo K a indpt obsvd rflns radiation (A = 0.71073 A) Fo 2 no(F,) ( n = 4.5) std. rflns std./ffln 20 scan range, 4.0-48.0 deg varin stds, % data collected f 1 0 , +14, +I8 (h.k,O Refinemento 4.04 A(@),e A-3 R(F), % 4.89 NdnS R(wF), % 0.001 GOF Nu(")
3047 2935 1989 3 stdl97 mns '1
0.33 10.9 1.02
23.7 (d, V p p = 4 Hz). Anal. Calcd for C~~HzsNioPz: C, 53.8; H, 7.09. Found: C, 54.0; H, 7.39. Reaction of 4 with CO. Using a procedure analogous to that described above for 3,a solution of 4 (0.32 g, 0.88 mmol) in benzene (20 mL) was stirred for 12 h under CO (1atm). Workup and chromatography gave 3 (0.04 g, 58%). Reaction of 5 with CO. Using a procedure analogous to that described above for 3, a solution of 5 (0.08 g, 0.21 mmol) in benzene (20 mL) was stirred for 12 h under CO (1atm). Workup and chromatography gave 3 (0.03 g, 82%). Preparation of 4,4-Dimethyl-3,4-&hydrocoumarin(9). To a solution of 5 (0.11 g, 0.27 mmol) in THF (20 mL) was added 1 2 (0.07 g, 0.27 mmol) under an Ar counterflow, causing an immediate color change from purple to dark yellow. The solution was stirred for 1 h at room temperature and then filtered. The filtrate was evaporated to dryness by using a rotary evaporator. The residue was extracted with ethyl acetate (30 mL), the extracts were concentrated, and chromatography on silica gel (eluent: n-hexandethyl acetate, 5:l) gave 4,4-dimethyl-3,4-dihydrocoumarin (9) (0.02 g, 55%). 'H NMR (CsDs): 6 6.99 (t, lH, aryl), 6.87 (d, 2H, aryl), 6.79 (t, lH, aryl), 3.93 (9, 2H, CHz), 1.04 (8, 6H, CH3). l3C NMR (C6D6, 125.7 MHz): 6 159.9 (aryl), 136.7 (aryl), 127.8 (aryl), 122.4 (aryl), 120.8 (aryl), 110.1 (aryl), 84.2 (CHZ),41.7 (CMed, 27.3 (CH3). EIMS m / z 148 (M+). Crystallographic Studies on 6. Crystal, data collection, and refinement parameters are given in Table 1. Suitable crystals of 6 were selected and mounted with epoxy cement to glass fibers. The unit-cell parameters were obtained by the least-squares refinement of the angular settings of 24 reflections (20"s 20 5 25"). The systematic absences in the diffraction data for 6 are uniquely consistent for the space group P21/n. The structure was solved using direct methods, completed by subsequent difference Fourier syntheses and refined by full-matrix least-squares procedures. All nonhydrogen atoms were refined with anisotropic displacement coefficients. Hydrogen atoms were treated as idealized contributions. All software and sources of the scattering factors are contained in either the SHEIXTL (5.1) or the SHEIXTL PLUS (4.2) program libraries (G. Sheldrick, Siemens XRD, Madison, WI).
Results and Discussion
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Nitrous oxide reacts slowly, over a period of 3 days
at 55 "C, with benzene solutions of (PMe&Ni(CHzCMez-
Koo et al.
458 Organometallics, Vol. 14,No. 1, 1995
Scheme 1
Q "'-
y.,.
1
Scheme 2 QPMe,
!
-
Ni
N-
-
1 reaction sequence for N2O consistent with mechanistic O-CsH4) (U5to give [ ( P M ~ ~ ) N I ( O - ~ - C ~ (21, H ~ C M ~proposals ~ C H ~ )made ~ ~ for the other heterocumulene insertions a product resulting from insertion of an oxygen atom is outlined in Scheme 2; the regiochemistry of the from N2O into a Ni-C bond of 1 (see Scheme 1) and insertion is controlled by the greater lability of the loss of PMe3 (as O=PMe3). The insertion reaction is phosphine ligand trans to C H Z . ~It is noteworthy that regiospecific, as judged by multinuclear NMR spectrosthe N20 oxidation of (C&e&Zr(PhC=CPh) to (C&e©, and the site of insertion was determined to be at Zr(OCPh=CPh) was shown to proceed via an isolable the Ni-aryl bond (not the Ni-alkyl linkage) by chemical NzO-inserted intermediate similar to the one proposed methods: (i) reaction of 2 with anhydrous HC1 gives 2-tert-butylphenolexclusively, and (ii)reaction of 2 with in Scheme 2, (C5Me&Zr(N(0)NCPh=CPh),3b although carbon monoxide gives only 4,4-dimethyl-2-oxo-W-lthe relevance of this electron-poor early-metal system benzopyran (3). Moreover, a derivative of 2 has been to the electron-rich nickel complex 1 is debatable. characterized by crystallographic methods, and the In the reaction of 1 with N20, it is somewhat surprisstructure confirms the atomic connectivity as depicted ing that not all of the PMe3 is oxidized to O=PMe3 (1 in Scheme 1 (vide infra). Formulation of 2 as a dimer equiv of PMe3 remains in the product, 2). In a control follows from the 1:l stoichiometric ratio of the CloH12.0 experiment it was found that free PMe3 is oxidized to ligand to the PMe3 ligand and by analogy to other O=PMe3 under the reaction conditions required for O-bridging dimeric products observed in reactions of l.5 formation of 2 (3 d, 55 "C). This result suggests that the remaining PMe3 ligand in 2 is one that does not The regiochemistry of O-insertion in the reaction of dissociate from Ni, and that N2O preferentially oxidizes 1 with N2O is consistent with observations of Carmona the Ni-C(ary1) bond over both the Ni-C(alky1) bond as et al., concerning the regiochemistry in addition reacwell as the coordinated PMe3 ligand. tions of heterocumulenes ((202, CS2, COS, PhNCS, Dimeric 2 reacts under mild conditions (20 "C, 30 min) This is in contrast to PhNCO, TolNCNTol) with with the chelating bidentate ligands 2,2'-bipyridine, 1,molecules without cumulated multiple bonds, like CO 10-phenanthroline, and 1,2-bis(dimethylphosphino)ethand H2C0, which react by inserting into the Ni-CH2 ane to afford the monomeric aryloxide complexes (bipy)b ~ n d . The ~ , ~observed regiochemistry in the N2O reacI tion might therefore have mechanistic significance since Ni(0-o0-Cd&CMe2CH2) (41, (phen)Ni(O-o-C&CMe&H2) it suggests (at least indirectly) that nitrous oxide reacts (51, and (dmpe)Ni(O-o-C6H4CMe2CH2)(6),respectively by inserting into the Ni-C bond as a heterocumulene r (i.e., NPN=O) and not by simply delivering its oxygen (see Scheme 3). It is interesting that neither (bipy)Niatom in a stepwise atom-transfer process. A possible I ( C H ~ C M ~ ~ - O - nor C ~ H(dmpe)Ni(CH2CMez-o-C&# ~)~ reacts with nitrous oxide to give 4 or 6, respectively, (6)Campora, J.; Gutibrrez, E.; Monge, A.; Palma, P.; Poveda, M. L.; Ruiz, C.; Carmona, E.Organometallics 1994, 13, 1728. findings consistent with reported observations that
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l . 5 8 6
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,
Syntheses and Reactions of New Nickel(II.1 Aryloxides
Organometallics, Vol.14,No. 1, 1995 459
Scheme 3
Y
c1131
a ,
c191
CI
CII
2
-
-
Figure 1. The molecular structure and atom-numbering
scheme for (dmpe)Ni(O-o-CsH4CMezCHz)(6).The hydrogen atoms have been omitted for clarity.
v
Table 2. Bond Lengths and Selected Bond Angles for 6
(dmpe)Ni(CHzCMez+CsH4) reacts much slower (and with differing reactivity) with heterocumulenes than does 1.6We have previously noted that the metallacycles (bipy)Ni{CHzC(CHz)C(CHz)CHz} and (bipy)Ni{(CHz)zCsH4}, both possessing sp2-hybridizedring carbons in the p-positions, show no reactivity toward N20, whereas similar (bipy)Ni-metallacycles having sp3hybridized ring carbons in the @-positionsuniformly react with NzO to give 0-transfer products.4b The fact that we can prepare 4 by an alternative route &e., from 2 bipy) lends support to our earlier speculation that the lack of reactivity of NzO with (bipy)nickelacycles having sp2$ carbons might be a consequence of prohibitive rigidity in these systems, and flexibility in the metallacycle could be important in allowing distortions required to accommodate the incoming N20 substrate.4b
Bond Lengths (A) 2.103( 1) Ni( 1)-P(2) 1.872(3) Ni( 1)-C( 1) 1.830(5) P( I)-C( 13) 1.802(6) P(2)-C( 12) 1.SO1(6) P(2)-C(16) 1.316(6) C( 1)-C(2) 1.524(6) C(2)-W 1.536(7) C(3)-C(4) 1.422(6) C(4)-C(6) 1.370(10) W)-C(7) 1.396(7) C(ll)-C(12)
+
P( 1)-Ni( 1)-P(2) P(2)-Ni( 1)-O( 1) P(2)-Ni( 1)-C( 1) Ni( 1)-0( 1)-C(8) C( l)-c(2)-c(3) C(3)-C(2)-C(9) C(3)-C(2)-C( 10) C(2)-C(3)-C(4) C(4)-C(3)-C(8) C(4)-C(5)-C(6) C(6)-C(7)-C(8) O( 1)-C(8)-C(7)
’
The structure of (dmpe)Ni(O-o-CsH4CMezCHz)(6)has been determined by single-crystal X-ray diffraction methods on crystals grown from pentane solution. Pertinent crystallographic data are given in Table 1,and bond lengths and selected bond angles are given in Table 2. A perspective view of 6 along with the atomlabeling scheme is shown in Figure 1. Monomeric 6 adopts a square-planar geometry about Ni. The most significant feature of the structure is that it allows for the unambiguous identification of the site of 0-atom insertion, i.e., a t the Ni-C(ary1) bond and not at the Ni-C(a1iphatic) bond. The salient metrical parameters found in 6 are very similar to the corresponding angles and distances found in the structure of the oxanickelacyclohexane complex (bipy)Ni{O(CH2)4} (7h4” The Ni(1)-0(1)bond in 6 (1.872(3)A) is somewhat longer than the Ni-0 bond in 7 (1.815(6) A), whereas the Ni-C bond lengths in 6 and 7 are, within experimental error, the same (Ni(1)-C(1) = 1.936(5) A in 6). In both structures, the CHZgroup exerts a more pronounced trans lengthening influence than does the OR group: in 6, Ni(1)-P(1) = 2.103(1) A (trans t o 0 ) and Ni(1)P(2) = 2.207(2)A (trans to CH2), a difference (A) of 0.10 A (in 7, A = 0.05 A). These trends are also manifested
Selected Bond Angles (deg) 87.6(1) P(1)-Ni(1)-O(1) 88.6(1) P(1)-Ni(1)-C(1) 173.9(1) O(1)-Ni(1)-C(1) 127.2(3) Ni(1)-C(1)-C(2) 110.5(4) C(l)-C(2)-C(9) 111.5(4) C(l)-C(2)-C(IO) 109.4(4) C(9)-C(2)-C(lO) 122.2(4) C(2)-C(3)-C(8) 118.2(4) C(3)-C(4)-C(5) 119.5(6) C(5)-C(6)-C(7) 121.4(4) O(I)-C(S)-C(3) 117.7(4) C(3)-C(S)-C(7)
2.207(2) 1.9360) 1.812(5) 1.836(6) 1.805(6) 1.548(6) 1.530(7) 1.373(7) 1.377(8) 1.376(9) 1.528(8) 173.31) 89.9(1) 94.4(2) 115.8(3) 108.2(4) 109.3(4) 107.9(4) 119.6(4) 122.5(5) 120.0(5) 123.9(4) 118.4(4)
Like 2, both 4 and 5 react with excess CO to give 3 (Scheme 4h7 It is noteworthy that the transformations of Schemes 1and 4,sequential addition of “ 0and “ C O to give 3 from 1, formally represent addition of the elements of COz. However, the sense of addition is reversed from that of direct addition of COSt o 1,where it is the C-atom of COZthat is attached to the aryl ring in 8 , not an 0-atom as is the case in our work. This is an intriguing observation that highlights the opportunities for obtaining unique transformations by utilizing an atom-transfer reaction coupled with a secondary reaction. For example, reactions involving 0-transfer from NzO coupled to addition of HZcould give products significantly different from those obtained by reaction of the same systems with Hz0. Reaction of 12 with 5 results in formal reductive elimination with formation of a new 0-C bond to give 4,4-dimethyl-3,4-dihydrocoumarin(9) in 55% yield (Scheme 4). Reductive elimination reactions that form (7) For other examples of CO-insertion, reductive elimination reac-
tions in related systems, see: (a) Kim, Y.-J.; Osakada, K.; Sugita, K.; in the structure of (PM~~)zN~{OC(O)-~-C~H~CM~ZCH~} Yamamoto, T.; Yamamoto, A. Organometallics 1988, 7 , 2182. (b) (8), the product of the reaction of 1 with COZ,where Komiya, S.; Akai, Y.; Tanaka, K; Yamamoto, T.; Yamamoto, A. Organometallics 1986, 4 , 1130. (c) References 4 and 6. Ni-0 = 1.877(9), Ni-C = 1.96(1), and A = 0.15
Koo et al.
460 Organometallics, Vol. 14, No.I, 1995
Scheme 4
Scheme 6 To I,
j
(bipy)Ni
(bipy)Ni
16 %
7 0-Et (bipy)Ni’
\
Et
(ref. 4 )
C-X bonds, where X is a heteroatom, are exceedingly rare.8 We have reported a few examples of such 0,Creductive eliminations in Ni(I1) systems, but the yields are uniformly low (-15-20 %) and limited to cyclic derivatives (see Scheme 5).4 The higher yield realized in the formation of 9 from 5 is an encouraging result that merits mechanistic investigation. It is noteworthy that similar reductive eliminations forming N-C bonds have been observed for related Ni(I1)compounds (Scheme 5),9and these unusual elimination reactions might be a consequence of weak Ni-NR2 and Ni-OR bonds in these electron-rich, late-metal complexes. Conclusions. Nitrous oxide has been found t o react
-
-
slowly, in a regioselective way with (PMe&Ni(CH2I
CMea-o-CsH4) (l),a square-planar Ni(I1) complex containing (i) two Ni-PMea bonds, (ii) a Ni-C(ary1) bond, and (iii) a Ni-C(aliphatic1 bond. The organometallic
sphere. The observed regiochemistry of the 0-insertion suggests, by analogy to literature precedent,6 that N20 reacts by inserting into 1 as a heterocumulene, and not by simple direct 0-transfer. Several monomeric derivatives of 2 have been prepared by reacting the dimer with chelating bidentate ligands, and the molecular structure
--
of one such derivative, (dmpe)Ni(O-o-CsH4CMe2CHz)(61, has been determined by X-ray crystallography.
The 1,lO-phenanthroline derivative (phen)Ni(O-oC6H4CMe2CH2) (5) reacts with I2 to effect formal 0,Creductive elimination to give the dihydrocoumarin 9 in good yield. Because of the unique nature of the reductive elimination to form a C-X bond in this and closely related we are actively investigating mechanistic details of this reaction.
Acknowledgment. We are grateful to the National Science Foundation for financial support of this research product, [(PM~~)N~(O-O-C~H~CM~~CH~)I~ (21, incorpothrough a grant t o G.L.H. (CHE-9200943) and to the rates only one 0-atom per Ni, and this appears as an government of South Korea for an Overseas Scholarship 0-insertion into the Ni-aryl bond. One equivalent of to K.K. PMe3 is oxidized to O=PMe3, and this probably occurs Supplementary Material Available: Tables of crystalto a phosphine that has dissociated from the metal, i.e., lographic details, atomic coordinates, bond angles and disthe oxidation occurs outside of the Ni coordination (8)Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (9) Koo, K.; Hillhouse, G. L., unpublished results.
tances, anisotropic thermal parameters, and hydrogen atom coordinates (8 pages). Ordering information is given on any current masthead page.
OM940658J
