Kinetically Directed Reactivity of Magnesium Dihydropyridides with

Feb 9, 2015 - Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, U.K. ... Marcus W. Drover , Laurel L. Schafer , Jennifer A. ...
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Kinetically Directed Reactivity of Magnesium Dihydropyridides with Organoisocyanates Michael S. Hill,* Dugald J. MacDougall, Gabriele Kociok-Köhn, Mary F. Mahon, and Catherine Weetman Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, U.K. S Supporting Information *

ABSTRACT: Although reactions between β-diketiminato magnesium species containing monocyclic 1,4-dihydropyridide ligands and the representative ketone benzophenone are observed to provide reduction by formal hydride transfer to yield magnesium diphenylphenoxide, similar reactions with organic isocyanates display only a very limited propensity toward hydride transfer and reduction to amidate species. In these latter systems, reaction primarily takes place with Mg−N insertion to afford O-bound ureide complexes. Further reactions of a magnesium dihydro-isoquinolide complex, which is constrained to hydride dearomatization at the 2-position only, display more variable behavior. Although similar Mg−N insertion and ureide formation is observed for reactions with isocyanates bearing less sterically demanding N-substitution, more bulky isocyanates provide unusual enamide C−C coupling reactivity.

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We have recently reported that well-defined β-diketiminato magnesium hydrides, prepared conveniently by reaction of PhSiH3 with the n-butyl magnesium complex II,6 react with a wide range of substituted and fused ring pyridine molecules to provide the corresponding dearomatized and reduced heterocyclic species (Scheme 1).7 In a subsequent advance we described extension of this reactivity to a catalytic regime to form N-borylated dihydropyridines through the use of pinacolborane (HBpin) as the reactive hydride source.8 Although similar reactivity has also been achieved with titanocene-,9 ruthenium-,10 and, very recently, lanthanumbased systems,11 the attractiveness of a magnesium-based protocol is underlined by the element’s earth abundance and negligible toxicity.12 Although alkaline-earth-based species such as compounds III−V displayed in Scheme 1 may be anticipated to behave as reactive hydride sources in a similar manner to I, studies of dihydropyridide derivatives of similarly electropositive group 3 elements have indicated that a much wider array of stoichiometric C−C coupling and C−H cleavage reactivity may be accessible.13 Irrespective of this possibility, compounds III−V may also be viewed as heterocyclic analogues of much better precedented dialkylamidomagnesium derivatives, which display deprotonation and insertion reactivity with protic or unsaturated substrate molecules, respectively. In this regard simple organoisocyanates, R′-NCO, provide an interesting case for assessment, as they combine both a potentially reducible carbonyl function and a well-established

INTRODUCTION Naturally occurring organohydride donors such as dihydronicotinamide adenine dinucleotide (NADH) and its phosphorylated analogue dihydronicotinamide adenine dinucleotide phosphate (NAD(P)H) are the primary biological reducing reagents for carbohydrate synthesis during the dark reactions of photosynthesis.1 While many bioinspired and organocatalytic NADH analogues, such as the long-known Hantzsch’s ester (HEH),2 are also well studied, the presence of a metal ion is often required to bind and activate substrate molecules to direct hydride attack from the NADH cofactor or analogue.3 Consequently the coordination and reaction chemistry of dihydropyridide coordination complexes has received considerable attention, with notable recent advances from across the periodic table.4

With respect to main group derivatives, the organohydride donor Lansbury’s reagent, [Li{Al(1,4-dihydropyrid-1-yl)4] (I),5 has been known to effect the selective reduction of ketones in the presence of carboxylic acid and ester groups for over 50 years. A significant factor in these reactions is the rearomatization of the pyridine ring system, and examples of s- or p-block dihydropyridide reactivity with retention of the reduced N-heterocyclic core are severely limited. © 2015 American Chemical Society

Special Issue: Mike Lappert Memorial Issue Received: December 4, 2014 Published: February 9, 2015 2590

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a

Dipp = 2,6-di-isopropylphenyl.

Scheme 2

resonance was observed at ca. δ 115 ppm in the 13C NMR spectra, which was assigned to the central sp2 carbon of the N2CO ureide ligand core. The retention of the sp3 methylene group in the 4-position of the heterocycle was also apparent through the persistence of a 2H multiplet signal at ca. δ 2.6 ppm in the 1H NMR spectra, while the alkenyl NCHCH and NCHCH resonances were observed as signals of a similar intensity at ca. 6.5 and 4.5 ppm, respectively. Although analogous treatment of III with tert-BuNCO at room temperature provided no discernible color change, heating of the solution at 80 °C for 12 h provided stoichiometric conversion to a single new magnesium-containing species, compound 5. This was identified as the formamidate species, formed by formal hydride addition to the carbon atom of the heterocumulene reagent, through the loss of all NMR signals corresponding to the 1,4-dihydropyridide ligand alongside a coincident increase in intensity of the signals associated with the free rearomatized pyridine. Analogous reactions performed with the 3-methylpyridine and 3,5-dimethylpyridine derivatives IV and V and the same range of organic isocyanates provided similar observations. Although all four reactions with compound IV resulted in direct Mg−N insertion and formation of magnesium ureide species (compounds 6−9, Scheme 2), compound V, containing the dimethyl-substituted dihydropyridide ligand, again provided evidence of different behavior. Addition of all four isocyanates to toluene solutions of V again resulted in instantaneous decolorization of the orange toluene solution of the dihydropyridide complex. Whereas for both aryl isocyanates and tertbutyl isocyanate, this process provided clean access to the ureide derivatives 10, 11, and 13, analysis by NMR spectroscopy indicated that reaction between 5 and AdNCO had resulted in the formation of two new products, 12a and 12b,

capacity for insertion into reactive metal−amide bonds.14 In this contribution, therefore, we present a survey of the reactivity of the magnesium derivatives of monocyclic 1,4-dihydropyridide derivatives III−V, along with the fused ring isoquinolide analogue VI, with a range of N-alkyl and N-aryl isocyanates, R/Ar−NCO.

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RESULTS AND DISCUSSION Reactivity of Monocyclic Magnesium 1,4-Dihydropyridide Derivatives. Compounds III−V were selected for study due to their diagnostically amenable 1H NMR spectra and the gradual adjustment to pyridine steric demands provided by the transition from the parent dihydropyridine derivative, III, to the corresponding 3-methyl- and 3,5-dimethylpyridines, compounds IV and V, respectively. The viability of hydride transfer from the magnesium 1,4-dihydropyridide derivatives to electrophilic carbon centers was demonstrated through an initial series of reactions between III−V and benzophenone, each of which provided facile access to the corresponding magnesium diphenylmethoxide (1, Scheme 2). Further reactions of compound III with the aryl isocynates DippNCO (Dipp = 2,6-di-isopropylphenyl) and MesNCO (Mes = 2,4,6-trimethylphenyl) and the alkyl isocyanates AdNCO (Ad = adamantyl) and tert-BuNCO provided some evidence for divergent behavior (Scheme 2). The distinctive orange-red coloration associated with the dihydropyridide anion was observed to discharge immediately upon addition of both aryl isocyanates and AdNCO to form pale yellow solutions of compounds 2−4. Analysis of compounds 2−4 by NMR spectroscopy evidenced the retention of the dearomatized 1,4-dihydropyridide fragment and allowed their identification as ureide derivatives formed by formal insertion of the respective heterocumulene into the Mg−N of the coordinated dihydropyride anion. In each case a 2591

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Figure 1. ORTEP representations of (a) compound 2 and (b) compound 13 with thermal ellipsoids set at the 25% level of probability. Hydrogen atoms except those attached to C(33) and the methyl groups of the β-diketiminate 2,6-di-isopropylphenyl substituents are removed for clarity. Selected bond lengths (Å) and angles (deg), 2: Mg(1)−N(1) 2.0528(15), Mg(1)−N(2) 2.0545(16), Mg(1)−O(1) 1.8921(13), Mg(1)−N(5) 2.1341(16), N(3)−C(30) 1.414(2), N(4)−C(30) 1.285(2), O(1)−C(30) 1.296(2), O(2)−Mg(1)−N(1) 121.70(6), O(2)−Mg(1)−N(2) 124.70(6), N(1)−Mg(1)−N(2) 94.34(6), O(2)−Mg(1)−N(5) 105.38(6), N(1)−Mg(1)−N(5) 106.86(6), N(2)−Mg(1)−N(5) 101.35(6), C(30)−O(2)−Mg(1) 147.97(11). 13: Mg(1)−N(1) 2.0442(15), Mg(1)−N(2) 2.0406(15), Mg(1)−O(1) 1.8804(12), Mg(1)−N(5) 2.1033(15), N(3)−C(30) 1.437(2), N(4)−C(30) 1.275(2), O(1)−C(30) 1.296(2), O(1)−Mg(1)−N(2) 114.99(6), O(1)−Mg(1)−N(1) 124.81(6), N(2)− Mg(1)−N(1) 93.29(6), O(1)−Mg(1)−N(5) 100.07(6), N(2)−Mg(1)−N(5) 111.93(6), N(1)−Mg(1)−N(5) 112.24(6), C(30)−O(1)−Mg(1) 158.59(12).

which the magnesium centers are five-coordinate.16 Although the C(30)−N(3) [2, 1.414(2); 13, 1.437(2) Å] and C(30)− N(4) [1, 1.285(2); 13, 1.275(2) Å] bonds to the nitrogen atoms arising from the 1,4-dihydropyridide and isocyanate reagents are consistent with localized single and double bonds, respectively, the coplanarity of the oxygen atoms, N(3), and N(4) with the sp2 C(30) carbon centers [∑(angles) = 360°] is, in both cases, indicative of significant delocalization across the ureide OCN2 units. The structure of compound 12b, wherein the asymmetric unit equates to one-quarter of a dimer molecule, is shown in Figure 2 with salient bond length and angle data presented in the figure caption. Compound 12b is a dimeric N-adamantyl formamidate, comprising two five-coordinate magnesium centers, each of which is coordinated by a β-diketiminate ligand, and an N,O-chelating formamidate ligand with dimer formation via μ2-O bridging interactions. Atoms Mg(1), O(1), N(2), C(16), H(16), and C(17) are located on a mirror plane implicit in the space group symmetry, and the full molecule is generated through a combination of this symmetry element plus the inversion center proximate to Mg(1). An additional ramification of the high symmetry is that all atoms, with the exception of the N-bound C(17) in the adamantane cage, are disordered over two sites. The bridging motif is reminiscent of that observed in the only previously reported magnesium amidate complex, the heterobimetallic acetamidate [Me2Al(iEt2N)2Mg{(Ph)NC(CH3)O}]2, and in the bridging R2NCO2− ligands in several magnesium carbamate structures.17,18 The central Mg2O2 ring within 12b displays similar Mg−O bond lengths [2.0013(18), 2.0785(18) Å], and the C(16)−N(2) distance [1.250(3) Å] is again indicative of significant localized imine character within the amidate ligand structure. Reactivity of Magnesium 1,2-Dihydroisoquinolide Derivatives. As appears to be the case for all reported organocatalytic and biologically occurring organohydride donors such as

which had formed in an approximate 30:70 ratio. Compounds 12a and 12b were characterized by the retention and loss of the dearomatized dihydropyridide fragment, respectively, leading to their assignment as the respective ureide and formamidate derivatives. These observations were confirmed by X-ray diffraction analyses performed on single crystals of the representative magnesium ureide compounds 2 and 13, which were isolated after crystallization from toluene solutions. A pure sample of compound 12b was also isolated by fractional crystallization and unambiguously assigned as a formamidate derivative by a further X-ray study. The results of the analyses of compounds 2 and 13 are displayed in Figure 1, while selected bond length and angle data are provided in the figure caption. Regardless of the N-bonded organic residue and substitution pattern of the dihydropyridide unit of the coordinated ureide ligand, the solid-state structures of compounds 2 and 13 display a number of common features. In both compounds the magnesium centers are four-coordinate with coordination spheres comprising the bidentate β-diketiminate ligands, a molecule of the relevant pyridine, and the ureide ligand, which binds exclusively through the oxygen donor atom. This coordination mode contrasts with that of the only previously described magnesium ureide derivative, the bimetallic species [(THF)3NaMg{(t-BuN)C(NPh2)(O)}3], in which all three of the ureide fragments coordinate to an octahedral magnesium center in a N,O-chelating fashion.15a The Mg−O distances in this previously described compound [2.1477(9) Å] are, however, also considerably elongated through a bridging interaction to sodium. The terminal Mg−O interactions within both 2 and 13 [2, 1.8921(13); 13, 1.8804(12) Å] are, thus, more closely comparable to those within Chisholm’s terminal β-diketiminato magnesium tert-butoxide [1.844(2) Å]15b and Fedushkin’s series of terminally oxygen-bound magnesium enolates supported by a 1,2-bis{(2,6-diisopropylphenyl)imino}acenaphthene ligand [range, 1.8902(19)−1.9212(18) Å], in 2592

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Figure 2. ORTEP representation compound 12b with thermal ellipsoids set at the 25% level of probability. Hydrogen atoms except those attached to C(16) and the methyl groups of the β-diketiminate 2,6-di-isopropylphenyl substituents are removed for clarity. Selected bond lengths (Å) and angles (deg): Mg(1)−O(1)′ 2.0013(18), Mg(1)−O(1) 2.0785(18), Mg(1)−N(1)″ 2.0839(13), Mg(1)−N(1) 2.0839(13), Mg(1)−N(2) 2.4344(18), O(1)−C(16) 1.312(3), O(1)′−Mg(1)−N(1)″ 110.49(5), O(1)−Mg(1)−N(1)″ 132.46(4), O(1)′−Mg(1)−N(1) 110.49(5), O(1)− Mg(1)−N(1) 132.46(4), N(1)″−Mg(1)−N(1) 92.29(7), O(1)′−Mg(1)−N(2) 130.69(7), O(1)−Mg(1)−N(2) 58.02(6), N(1)″−Mg(1)−N(2) 103.01(5), N(1)−Mg(1)−N(2) 103.01(5). Symmetry transformations used to generate equivalent atoms: ′ −x + 2, y, −z + 1; ″ x, −y, z; ‴ −x + 2, −y, −z + 1.

Scheme 3

NADH,19 compounds III−V contain thermodynamically preferred 1,4-dihydropyridide ligands. Although this observation implies that 1,4-dearomatization is a necessity for hydrogen transfer reactivity, the potential for similar behavior is precedented by several reactivity studies of 1,2-dihydropyridide ligands bound to electropositive d0 centers. Most pertinently, Harder and co-workers have recently observed intramolecular hydride transfer between a 1,2-dihydropyridide anion and a coordinated and perdeuterated pyridine molecule.7c Similarly Diaconescu and co-workers have demonstrated that group 3-mediated reactions of ketones with dearomatized isoquinolines, in which 1,4-dearomatization is blocked by the fused aromatic system, occur with reduction to the corresponding alkoxide.20 A reaction between the previously reported isoquinolide complex VI and benzophenone was thus undertaken

and, in a manner reminiscent of compounds III−V, was observed to again provide facile access to compound 1 and rearomatization of the N-heterocycle. Reactions between VI and the less sterically demanding organic isocyanates i-PrNCO and EtNCO provided ureide derivatives (14, 15) analogous to the crystallographically confirmed compounds 2 and 13 (Scheme 3). In both cases the continued integrity of the dearomatized isoquinolide heterocycle within the ureide anion was clearly apparent through the retention of correlated (HSQC) methylene resonances at ca. 5 and ca. 50 ppm in the respective 1H and 13C NMR spectra. These assignments were supported by a subsequent singlecrystal X-ray diffraction analysis performed on a sample of compound 14. The results of this analysis (Figure 3) and the resultant bond length and angle data, while confirming the 2593

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Figure 3. ORTEP representation of compound 14 with thermal ellipsoids set at the 25% level of probability. Hydrogen atoms except those attached to C(34) and isopropyl groups of the β-diketiminate 2,6-di-isopropylphenyl substituents are removed for clarity. Selected bond lengths (Å) and angles (deg): Mg(1)−N(1) 2.0344(14), Mg(1)−N(2) 2.0368(14), Mg(1)−O(1) 1.8787(12), Mg(1)−N(5) 2.1129(15), N(3)−C(30) 1.283(2), N(4)−C(30) 1.421(2), O(1)−C(30) 1.3013(2), O(1)−Mg(1)−N(1) 123.84(6), O(1)−Mg(1)−N(2) 118.24(6), N(1)−Mg(1)−N(2) 94.25(6), O(1)−Mg(1)−N(5) 102.39(6), N(1)−Mg(1)−N(5) 107.62(6), N(2)−Mg(1)−N(5) 110.10(6), C(30)−O(1)−Mg(1) 151.91(11), C(2)−N(1)− C(18) 118.51(13), C(2)−N(1)−Mg(1) 121.16(11), C(18)−N(1)−Mg(1) 120.28(10).

formation of an unusual isoquinolide-based ureide anion, are otherwise unremarkable and are closely comparable to those discussed above for compounds 2 and 13. Similar treatment with alkyl isocyanates bearing more sterically encumbered nitrogen substitution, however, provided a different course of reaction. Reactions of tert-butyl and adamantyl isocyanates with VI to produce compounds 16 and 17 (Scheme 3) again took place with retention of the isoquinolide methylene signals at δ 4.12 and 3.54 ppm in the respective 1H NMR spectra. The mutually coupled doublet signals observed at δ 6.4 and 5.6 ppm in the 1H NMR spectrum of VI associated with the methine protons attached to C3 and C4 of the dearomatized N-heterocycle were, however, observed to be replaced by singlet resonances corresponding to 1H by integration of the peak intensities at δ 5.86 (16) and 6.63 (17) ppm. In addition, the same spectrum of 16 was observed to comprise a further broadened (N-H) singlet resonance of the same intensity at 4.14 ppm. The origin of these observations was resolved through the isolation of crystals of compound 17 suitable for single-crystal X-ray diffraction analysis, the results of which are illustrated in Figure 4, with selected bond length and angle data provided in the figure caption. Compound 17 displays a dodecameric heterocyclic structure constructed through the dimerization of two β-diketiminato magnesium derivatives of a dearomatized isoquinolide anion in which the C4 carbon centers (labeled C(37) and C(87) in Figure 4) of the N-heterocyclic rings are bonded to an N-adamantyl primary amide residue. The dimagnesium heterocyclic structure is propagated through formally anionic covalent Mg−N [Mg(1)−N(3) 2.0627(15), Mg(2)−N(7) 2.0593(15) Å] bonds to the isoquinolide ring

nitrogen centers and formally dative covalent Mg−O [Mg(1)− O(1) 1.9670(12), Mg(2)−O(2) 1.9530(12) Å] interactions to the carbonyl groups of the adamantyl amide substituents. Although the various C−C and C−N bond distances and angles within the structure are unexceptional, the continued deraomatization of the substituted isoquinoline units is unambiguously demonstrated by the variation in the formally single- and double-bonded distances and the non-coplanarity of the C30 and C80 methylene carbon centers and the remaining atoms of the N-heterocyclic units. These observations indicate that the outcome of the reactions between compound VI and N-aliphatic isocyanates is dictated by the steric demands of the N-alkyl substituent and the resultant kinetic preference toward either insertion into the Mg−N bond to provide ureide species or addition at the C4 methine proton by the isocyanate electrophile. Variations in Nsubstituent identity have been reported to provide only minor inductive modulation of the basicity of organic isocyanates.21 We suggest, therefore, that the major contributing factor to the emergence of this divergent reactivity is the relative ability of the isocyanate to precoordinate to the Mg center. It has been demonstrated previously that related carbodiimide precoordination to lithium or aluminum amides is a crucial reaction step during catalytic guanylation reactions.22 Less sterically demanding substrates such as N-ethyl and N-isopropyl isocyanate are, thus, able to precoordinate with subsequent intramolecular N−C bond formation through migration of the nucleophilic isoquoinolide to the central sp carbon center of the isocyanate (Scheme 4). Enamines and enamide derivatives are known to behave as potent carbon-based nucleophiles,23 which may be employed in a host of C−C bond forming processes through 2594

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Figure 4. ORTEP representation of compound 17 with thermal ellipsoids set at the 25% level of probability. Hydrogen atoms except those attached to C(30), C(80), N(4), and N(8) and isopropyl groups of the β-diketiminate 2,6-di-isopropylphenyl substituents are removed for clarity. Selected bond lengths (Å) and angles (deg): Mg(1)−N(1) 2.0547(15), Mg(1)−N(2) 2.0703(14), Mg(1)−O(1) 1.9670(12), Mg(1)−N(3) 2.0627(15), N(3)−C(30) 1.483(2), N(4)−C(39) 1.348(2), O(1)−C(39) 1.2722(19), O(1)−Mg(1)−N(1) 108.94(6), O(1)−Mg(1)−N(3) 120.92(6), N(1)− Mg(1)−N(3) 109.17(6), O(1)−Mg(1)−N(2) 102.46(5), N(1)−Mg(1)−N(2) 92.81(6), N(3)−Mg(1)−N(2) 118.77(6), O(2)−Mg(2)−N(6) 105.94(6), O(2)−Mg(2)−N(5) 111.15(6), N(6)−Mg(2)−N(5) 92.49(6), O(2)−Mg(2)−N(7) 117.35(6), N(6)−Mg(2)−N(7) 115.62(6), N(5)− Mg(2)−N(7) 111.51(6).

Scheme 4

reaction with carbonyl-containing reagents.24 In the cases of reactions between VI and the more sterically demanding tertbutyl and adamantyl isocyanates, precoordination to magnesium is hindered, resulting in more kinetically favored nucleophilic attack of the enamide CC double bond at the electrophilic isocyanate carbon center (Scheme 4). In summary, we have observed that well-defined magnesium 1,4-dihydropyridide species react with organic isocyanates primarily through resultant Mg−N insertion to afford O-bound ureide complexes. Although reactions with the representative ketone benzophenone provide reduction by formal hydride transfer to yield the diphenylphenoxide, similar reactions with isocyanates display only a very limited propensity toward hydride transfer and reduction to amidate species. In contrast to this relatively straightforward behavior, reactions of a magnesium dihydroisoquinolide complex, which is constrained to hydride dearomatization at the 2-position only, display more variable reactivity. In these cases Mg−N insertion with ureide formation is observed for reactions with isocyanates bearing less sterically demanding N-substitution, whereas more bulky isocyanates

provide unusual enamide C−C coupling reactivity. We are continuing to study the reactivity of these readily accessed dihydropyridide species with alternative heterocumulene and unsaturated reagents.

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EXPERIMENTAL SECTION

All reactions were carried out using standard Schlenk line and glovebox techniques under an inert atmosphere of either nitrogen or argon. NMR experiments were conducted in Youngs tap NMR tubes, made up and sealed in a glovebox. NMR spectra were collected on a Bruker AV300 spectrometer operating at 75.5 MHz (13C). The spectra were referenced relative to residual solvent resonances. Mass spectrometry was performed on a Bruker Daltonik microTOF electrospray time-of-flight (ESI-TOF) mass spectrometer coupled to an Agilent 1200 LC system as an autosampler. A 10 μL amount of sample was injected into a 30:70 flow of water/methanol at 0.4 mL/min followed by injection of 10 μL of 5 mM sodium formate to act as a calibrant over the mass range 50−1500 m/z. Solvents (toluene, hexane) were dried by passage through a commercially available (Innovative Technologies) solvent purification system under nitrogen and stored in ampules over molecular sieves. C6D6 and d8-toluene were purchased 2595

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Article

Organometallics

24.7, 24.0, 23.8 (NCHCHCH2), 21.8. Despite repeated attempts, an acceptable elemental analysis could not be obtained for this highly airand moisture-sensitive compound. HRMS (ESI): calcd for hydrolyzed product [M+]+ C16H23N2O m/z 259.37, found 259.1810; [M+Na+]+ C16H22N2NaO m/z 281.35, found 281.1629. Compound 5. A toluene solution of compound III (50 mg, 0.08 mmol) and t-BuNCO (9.5 μL, 0.08 mmol) was heated at 80 °C for 12 h. Concentration of the reaction solution in vacuo provided compound 5 as pale yellow crystals (20 mg, 22%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 7.14−7.07 (6H, m, Ar-H), 7.03 (1H, s, NCHO), 4.89 (1H, s, NC(CH3)CH), 3.32 (4H, m, CH(CH3)2), 1.67 (6H, s, NC(CH3)CH), 1.29 (9H, s, C(CH3)3), 1.22 (12H, d, JHH = 7.2 Hz, CH(CH3)2), 1.16 (12H, d, JHH = 6.8 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 171.3 (NC(CH3)CH), 143.1, 136.8 (p-Ar), 129.7 (NCHO), 128.9, 126.2 (m-Ar), 93.8 (NC(CH3)CH), 29.0 (CH(CH3)2), 24.8 (NC(CH3)CH), 23.8 (CH(CH3)2), 21.8 (C(CH3)3). Anal. Calcd (found) for C44H61MgN5O: C 75.46 (75,34); H 8.78 (8.78); N 10.00 (9.86). Compound 6. A toluene solution of compound IV (50 mg, 0.08 mmol) was stirred with DippNCO (17 μL, 0.08 mmol) at room temperature. Removal of solvent in vacuo yielded an analytically pure yellow oil (42 mg, 61%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 8.03 (1H, o-3-Pic), 7.90 (1H, o-3-Pic), 7.21−7.02 (9H, m, ArH), 6.98 (1H, s, NCH), 6.81 (3H, m, NCH, m-DippH(NCO)), 6.72 (1H, d, JHH = 9 Hz, p-3-Pic), 6.47 (1H, m, m-3-Pic), 4.95 (1H, s, NC(CH3)CH), 4.45 (1H, m, NCHCH), 3.27 (4H, m, CH(CH3)2), 2.67 (2H, m, CH(CH3)2), 2.59 (2H, m, NCHCHCH2), 1.71 (6H, s, NC(CH3)CH), 1.66 (3H, s, 3-(CH3)Pyr), 1.42 (3H, s, NCHC(CH3)), 1.16 (12H, d, JHH = 9 Hz, CH(CH3)2), 1.07 (12H, d, JHH = 9 Hz, CH(CH3)2), 0.81 (6H, d, JHH = 6 Hz, CH(CH3)2(NCO)). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 169.3 (NC(CH3)CH), 150.1 (o-3-Pic), 146.8 (o-3-Pic), 145.7, 142.6, 141.0, 138.3, 133.8, 126.4, 125.5, 124.0, 123.7, 122.8, 121.8, 115.8 (OCN), 100.9 (NCHCH), 94.6 (NC(CH3)CH), 28.5, 28.4, 28.1, 24.5, 24.4, 24.3, 24.2, 23.8 (NCHCHCH2). Anal. Calcd (found) for C54H73MgN5O: C 77.91 (77.71); H 8.84 (8.94); N 8.41 (8.32). HRMS (ESI): calcd for hydrolyzed product [M]+ C19H26N2O m/z 298.43, found 299.2124. Compound 7. A toluene solution of compound IV (300 mg, 0.47 mmol) was stirred with MesNCO (77 mg, 0.47 mmol) at room temperature. Concentration to incipient crystallization yielded compound 7 as yellow crystals (221 mg, 59%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 8.51 (1H, m, o-3-Pic), 8.41 (1H, m, o-3Pic), 7.02 (1H, m, p-3-pic), 6.98 (1H, m, NCH), 6.92 (1H, s, NCH), 6.78 (2H, m, p-ArH), 6.68 (m-3-pic), 6.59 (4H, m, m-ArH), 6.42 (2H, s, m-Mes-H), 4.97 (1H, s, NC(CH3)CH), 4.30 (1H, m, NCHCH), 3.25 (2H, m, CH(CH3)2), 2.94 (2H, m, CH(CH3)2), 2.42 (2H, m, NCHCHCH2), 2.08 (6H, s, o-CH3Mes), 1.75 (3H, s, p-CH3Mes), 1.73 (6H, s, NC(CH3)CH), 1.58 (6H, s, CH3-3-Pic), 1.17 (12H, d, JHH = 7.23 Hz, CH(CH3)2), 1.03 (12H, d, JHH = 6.63 Hz, CH(CH3)2). 13 C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.1 (NC(CH3)CH), 146.2 (o-3-Pic), 142.6 (o-3-Pic), 136.3, 133.5, 131.6, 125.2, 123.8, 123.3, 115.0 (OCN), 102.0 (NCHCH), 94.7 (NC(CH3)CH), 28.4 (CH(CH3)2), 24.5 (NC(CH3)CH), 24.3 (CH(CH3)2), 23.1 (CH(CH3)2), 20.8 (CH3-Mes), 20.8 (CH3-Mes), 18.4 (CH3-3-Pic), 17.8 (CH3-3-Pic(H)). Despite repeated attempts, an acceptable elemental analysis could not be obtained for this highly airand moisture-sensitive compound. HRMS (ESI): calcd for hydrolyzed product [M]+ C16H20N2O m/z 256.34, found 257.1654; [M+Na+]+ C16H20N2NaO m/z 279.34, found 279.1473. Compound 8. A toluene solution of compound IV (50 mg, 0.08 mmol) was stirred with AdNCO (14 mg, 0.08 mmol) at room temperature. Concentration to incipient crystallization yielded compound 8 as yellow crystals (38 mg, 59%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 8.37 (2H, m, o-3-Pic), 7.48 (1H, s, NCH), 7.39 (1H, m, NCH), 7.23−6.98 (6H, m, Ar-H), 6.59 (1H, m, p-3-Pic), 6.23 (1H, m, m-3-Pic), 5.01 (1H, s, NC(CH3)CH), 4.71 (1H, m, NCHCH), 3.90 (1H, m, CH-Ad), 3.67 (2H, m, CH(CH3)2), 3.08 (2H, m, NCHCHCH2), 3.04 (2H, m, CH(CH3)2), 1.77 (6H, s, CH3-3-Pic, CH3-3-Pic(H)), 1.74 (6H, s, NC(CH3)CH), 1.44 (6H, d, JHH = 6.65 Hz, CH(CH3)2), 1.34 (6H, d, JHH = 6.65 Hz, CH(CH3)2),

from Goss Scientific Instruments Ltd. and dried over molten potassium before distilling under nitrogen and storing over molecular sieves. CHN microanalysis was performed by Stephen Boyer of London Metropolitan University. Compounds II−VI were synthesized by literature procedures.7 Compound 1. Compound III (300 mg, 0.5 mmol) was reacted with benzophenone (91 mg, 0.5 mmol) for 1 h at room temperature in hexanes (5 mL). The orange color of the solution was immediately discharged, and compound 1 was isolated as a colorless microcrystalline solid after concentration of the solution (290 mg, 92%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 7.36−7.00 (16H, m, Ar-H), 6.15 (1H, s, OCH), 5.0 (1H, s, NC(CH3)CH), 3.25 (4H, m, CH(CH3)2), 1.81 (6H, s, NC(CH3)CH), 1.15 (12H, d, JHH = 6 Hz, CH(CH3)2), 0.79 (12H, brs, CH(CH3)2). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 169.4 (NC(CH3)CH), 152.7, 145.8, 142.9, 136.5, 128.2, 126.7, 125.7, 124.3, 94.2 (NC(CH3)CH), 78.6 (OCH), 28.9 (CH(CH3)2), 24.7 (CH(CH3)2), 24.5 (NC(CH3)CH). Anal. Calcd (found) for C42H52MgN2O: C 80.69 (80.86); H 8.38 (8.40); N 4.48 (4.53). Compound 2. A toluene solution of compound III (300 mg, 0.5 mmol) and DippNCO (106.8 μL, 0.5 mmol) was stirred for 1 h at room temperature. In vacuo removal of solvent and recrystallization from hexanes at −30 °C provided compound 2 as colorless crystals (130 mg, 33%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 8.43 (2H, m, o-Pyr), 7.21−6.98 (9H, m, Ar-H), 6.89 (2H, m, p-Pyr), 6.71 (2H, m, NCHCH), 6.56 (2H, m, m-Pyr), 5.02 (1H, s, NC(CH3)CH), 4.42 (2H, m, NCHCH), 3.33 (4H, m, CH(CH3)2), 2.76 (2H, m, NC(CH(CH3)2), 2.66 (2H, m, NCHCHCH2), 1.74 (6H, s, NC(CH3)2), 1.25−1.16 (30H, m, CH(CH3)2), 0.93 (6H, d, JHH = 9 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 170.2 (NC(CH3)CH), 150.4 (o-Pyr), 145.5, 143.0 (p-DippL), 142.0, 136.8 (p-Pyr), 127.0 (NCHCH), 126.1, 124.6 (m-DippL), 124.2 (m-Pyr), 123.7, 115.2 (OCN), 103.0 (NCHCH), 95.3 (NC(CH3)CH), 28.8 (NC(CH(CH3)2), 28.6 (CH(CH3)2), 25.0 (CH(CH3)2), 24.7 (CH(CH3)2), 24.5 (NC(CH3)CH), 24.1 (CH(CH3)2), 23.5 (CH(CH3)2), 23.1 (NCHCHCH2). Anal. Calcd (found) for C52H69MgN5O: C 77.54 (77.67); H 8.76 (8.72); N 8.69 (8.80). HRMS (ESI): calcd for hydrolyzed product [M+Na+]+ C18H24N2NaO m/z 307.18, found 307.1786. Compound 3. A toluene solution of compound III (50 mg, 0.08 mmol) and MesNCO (13.4 mg, 0.08 mmol) was stirred at room temperature for 12 h. Concentration of the reaction solution in vacuo provided compound 3 as pale yellow crystals (41 mg, 67%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 8.58 (2H, m, o-Pyr), 7.14−6.99 (6H, m, Ar-H), 6.92 (1H, m, p-Pyr), 6.61 (4H, m, m-Mes-H, m-Pyr), 6.44 (2H, m, NCHCH), 4.96 (1H, s, NC(CH3)CH), 4.26 (2H, m, NCHCH), 3.22 (4H, m, CH(CH3)2), 2.54 (2H, m, NCHCHCH2), 2.11 (6H, s, o-CH3(Mes)), 1.73 (6H, s, NC(CH3CH), 1.62 (3H, s, p-CH3(Mes)), 1.28−0.85 (24H, m, CH(CH3)2). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 169.2 (NC(CH3)CH), 150.2 (o-Pyr), 148.3, 146.3, 142.4, 125.2 (NCH), 123.9 (m-Pyr), 116.2 (OCN), 106.4 (NCHCH), 94.7 (NC(CH3)CH), 28.8 (p-CH3(Mes)), 28.5 (o-CH3(Mes)), 24.4 (CH(CH3)2), 24.3 (NC(CH3)CH), 24.2 (CH(CH3)2), 24.0 (CH(CH3)2), 22.6 (NCHCHCH2), 20.8(CH(CH3)2). Anal. Calcd (found) for C49H63MgN5O: C 77.20 (77.05); H 8.33 (8.41); N 9.19 (9.12). Compound 4. A toluene solution of compound III (50 mg, 0.08 mmol) was stirred with AdNCO (15 mg, 0.08 mmol) at room temperature. Concentration to incipient crystallization yielded compound 4 as colorless crystals (32 mg, 52%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 8.53 (2H, s, o-Pyr), 7.23−7.00 (6H, m, Ar-H), 6.66 (1H, m, p-Pyr), 6.63 (2H, m, m-Pyr), 6.51 (2H, m, NCHCH), 4.99 (1H, s, NC(CH3)CH), 4.51 (2H, m, NCHCH), 3.72 (1H, m, NCH(Ad)), 3.32 (4H, m, CH(CH3)2), 2.63 (2H, m, NCHCHCH2), 1.71 (6H, s, NC(CH3)CH), 1.51−1.37 (15, m, Ad-H), 1.22 (12H, d, JHH = 7.2 Hz, CH(CH3)2), 1.16 (12H, d, JHH = 6.8 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, C6D6, 300 K) δC (ppm): 170.0 (NC(CH3)CH), 148.9 (o-Pyr), 143.2, 129.7, 126.0, 125.4 (NCH), 124.0 (m-Pyr), 104.2 (NCHCH), 94.6 (NC(CH3)CH), 29.0 (NCH(Ad)), 28.7 (CH(CH3)2), 26.2 (Ad-C), 25.0 (NC(CH3)CH), 24.9, 2596

DOI: 10.1021/om5012374 Organometallics 2015, 34, 2590−2599

Article

Organometallics

Compound 12b. A toluene solution of compound V (330 mg, 0.50 mmol) was stirred with AdNCO (89 μL, 0.50 mmol) at room temperature. Concentration to incipient crystallization yielded compound 12b as pale yellow crystals (216 mg, 70%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 7.04−6.74 (12H, m, Ar-H), 6.19 (2H, s, NCHO), 4.84 (2H, s, NC(CH3)CH), 3.29 (2H, m, CH(CH3)2), 3.10 (3H, m, CH(CH3)2), 2.92 (3H, m, CH(CH3)2), 2.41 (12H, d, J HH = 6 Hz, CCH 2CHCH 2), 2.21 (6H, m, CCH2CHCH2), 1.96 (6H, s, NC(CH3), 1.65 (6H, s, NC(CH3)), 1.43 (12H, d, JHH = 6 Hz, CCH2CHCH2), 1.25 (18H, d, JHH = 9 Hz, CH(CH3)2), 1.19 (18H, d, JHH = 6 Hz, CH(CH3)2), 0.89 (12H, d, JHH = 9 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.70 (NCHO) 148.61, 146.69, 146.49, 146.23, 145.26, 144.90, 142.57, 142.36, 140.93, 135.13, 125.92, 125.73, 125.42, 123.99, 123.73, 122.97, 105.42 (NC(CH3)CH), 96.45, 51.32 (NCCH2), 46.40 (NCCH2), 38.46 (NCCH2CH), 30.98 (NCCH2CHCH2), 29.11, 28.77, 28.54, 28.32, 25.77, 25.63, 25.33, 25.21, 25.10, 24.96, 24.69, 24.58, 24.40, 23.74, 21.70 (CH(CH3)2), 21.05 (CH(CH3)2), 18.05 (CH(CH3)2). Anal. Calcd (found) for C40H57MgN3O: C 77.46 (77.52); H 9.26 (9.18); N 6.78 (6.85). Compound 13. A toluene solution of compound V (330 mg, 0.50 mmol) was stirred with t-BuNCO (52.4 μL, 0.50 mmol) at room temperature. Concentration to incipient crystallization yielded compound 13 as yellow crystals (210 mg, 55%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 7.40 (2H, s, o-H (3,5-Lut)), 7.23−6.98 (6H, m, Ar-H), 6.85 (2H, s, o-H (3,5-Lut(H))), 6.49 (1H, s, p-H (3,5-Lut)), 5.05 (1H, s, NC(CH3)CH), 3.63 (2H, m, CH(CH3)2), 3.13 (2H, m, CH(CH3)2), 2.92 (2H, s, NCHC(CH3)CH2), 1.83 (6H, s, NCHC(CH3)CH), 1.81 (6H, s, NCHC(CH3)CH2), 1.57 (6H, s, NC(CH3)), 1.38 (6H, d, JHH = 6 Hz, CH(CH3)2), 1.28 (6H, d, JHH = 6 Hz, CH(CH3)2), 1.11 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.93 (9H, s, C(CH3)3), 0.72 (6H, d, JHH = 9 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.15 (o-Pyr), 146.55, 145.88, 141.95, 140.46, 137.44, 134.36, 123.29, 104.86 (NC(CH3)CH), 95.62 (NCHC(CH3)CH2), 31.08 (NCHC(CH3)CH2), 28.69 (CH(CH3)2), 28.44 (CH(CH3)2), 24.99 (CH(CH3)2), 24.74 (CH(CH3)2), 24.14 (NCHC(CH3)CH2), 17.52 (C(CH3)3). Anal. Calcd (found) for C48H69MgN5O: C 76.22 (76.05); H 9.19 (9.11); N 9.26 (9.16). HRMS (ESI): calcd for hydrolyzed product [M+Na+]+ C12H20N2NaO m/z 231.15, found 231.1473. Compound 14. A toluene solution of compound VI (100 mg, 0.14 mmol) was stirred with i-PrNCO (14 μL, 0.14 mmol) at room temperature. Concentration to incipient crystallization yielded compound 14 as yellow crystals (34 mg, 31%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 9.15 (1H, s, o-H iQuin), 8.43 (1H, s, o-H iQuin), 7.22−6.82 (15H, m, Ar-H), 6.33 (1H, d, JHH = 6 Hz, NCH), 5.58 (1H, d, JHH = 6 Hz, NCHCH), 5.37 (2H, s, NCH2), 5.03 (1H, s, NC(CH3)CH), 3.59 (2H, m, CH(CH3)2), 3.21 (1H, m, CH(CH3)2), 2.84 (2H, m, CH(CH3)2), 1.78 (6H, s, NC(CH3)2), 1.51 (6H, d, JHH = 9 Hz, CH(CH3)2), 1.27 (6H, d, JHH = 6 Hz, CH(CH3)2), 1.09 (6H, d, JHH = 6 Hz, NCH(CH3)2), 1.00 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.14 (6H, d, JHH = 6 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 170.3 (NC(CH3)CH), 152.3 (o-CH iQuin), 150.3 (NCH), 145.3, 143.3, 139.7 (o-CH iQuin), 136.8, 135.2, 131.5, 130.7, 127.4, 126.7, 126.2, 125.1, 124.3, 123.2, 95.7 (NCHCH), 94.7 (NC(CH3)CH), 48.20 (NCH2), 46.4 (NCH(CH3)2), 29.4 (CH(CH3)2), 28.5 (CH(CH3)2), 26.9 (NCH(CH3)2)), 25.2 (CH(CH3)2), 24.9 (CH(CH3)2), 24.6 (NC(CH3)CH), 24.5 (CH(CH3)2), 24.4 (CH(CH3)2). Despite repeated attempts, an acceptable elemental analysis could not be obtained for this highly air- and moisture-sensitive compound. Compound 15. A toluene solution of compound VI (100 mg, 0.14 mmol) was stirred with EtNCO (11 μL, 0.14 mmol) at room temperature. Concentration to incipient crystallization yielded compound 15 as yellow crystals (40 mg, 37%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 9.53 (1H, s, o-H iQuin), 8.78 (1H, s, o-H iQuin), 7.39−6.82 (15H, m, Ar-H), 6.63 (1H, d, JHH = 6 Hz, NCH), 5.65 (1H, d, JHH = 9 Hz, 5.18 (1H, s, NC(CH3)CH), 4.94 (2H, s, NCH2), 3.36 (3H, m, CH(CH3)2), 2.86 (1H, m, CH(CH3)2), 2.26 (2H, q, JHH = 9 Hz, NCH2CH3), 1.90 (6H, s, NC(CH3)CH),

1.10 (6H, d, JHH = 7.02 Hz, CH(CH3)2), 0.68 (6H, d, JHH = 7.02 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.4 (NC(CH3)CH), 146.0 (o-3-Pic), 144.9 (o-3-Pic), 141.9 (o-3Pic(H)), 135.3, 125.7, 125.0, 123.4, 117.7 (OCN), 105.7 (NCHCH), 97.1 (NC(CH3)CH), 44.6 (CH-Ad), 37.5, 35.7, 30.6 (NCHCHCH2), 28.6 (CH(CH3)2), 28.4 (CH(CH3)2), 25.6 (CH(CH3)2), 24.7 (NC(CH3)CH), 24.5 (CH(CH3)2), 24.2 (CH(CH3)2), 23.4 (CH(CH3)2), 17.8 (CH3-3-Pic), 17.7 (CH3-3-Pic(H)). Anal. Calcd (found) for C52H71MgN5O: C 77.44 (77.32); H 8.87 (8.73); N 8.68 (8.57). Compound 9. A toluene solution of compound IV (50 mg, 0.08 mmol) was stirred with t-BuNCO (9 μL, 0.08 mmol) at room temperature. Concentration to incipient crystallization yielded compound 9 as yellow crystals (40 mg, 69%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 8.19 (1H, brs, NCHC(CH3)CH), 7.55 (1H, brs, NCHCHCH2), 7.32 (1H, brs, NCHCHCH), 7.20−6.98 (7H, m, Ar-H), 6.56 (1H, brs, p-H (3-Pic)), 6.20 (1H, brs, m-H (3-Pic)), 5.01 (1H, s, NC(CH3)CH), 4.71 (1H, m, NCHCHCH2), 3.62 (2H, m, CH(CH3)2), 3.12 (2H, m, CH(CH3)2), 3.07 (2H, brs, NCHCHCH2), 1.76 (6H, s, NC(CH3)CH), 1.40 (12H, d, JHH = 9 Hz, CH(CH3)2), 1.09 (12H, d, JHH = 9 Hz, CH(CH3)2), 0.94 (9H, s, C(CH3)3). 13 C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.3 (NC(CH3)CH), 149.5 (o-C (3-Pic)), 148.6 (o-C (3-Pic)), 145.8, 144.8, 143.6, 142.7, 141.9 (o-C (3-Pic(H)), 140.0, 124.3, 123.4, 105.7 (NCHCHCH 2 ), 97.2 (NC(CH 3 )CH), 50.0 (C(CH 3 ) 3 ), 31.5 (NCHCHCH2), 28.6 (CH(CH3)2), 28.4 (CH(CH3)2), 25.2, 24.6, 24.2, 23.4, 21.4 (C(CH3)3), 17.6 (CH3 (3-Pic(H)). Anal. Calcd (found) for C46H65MgN5O: C 75.86 (75.69); H 9.00 (9.14); N 9.62 (9.55). Compound 10. A toluene solution of compound V (50 mg, 0.08 mmol) was stirred with DippNCO (17 μL, 0.08 mmol) at room temperature. Concentration to incipient crystallization yielded compound 10 as yellow crystals (40 mg, 63%). 1H NMR (300 MHz, d8Tol, 300 K) δH (ppm): 7.87 (2H, s, o-H (3,5-Lut)), 7.17−7.07 (12H, m, Ar-H), 6.98 (1H, s, p-H (3,5-Lut)), 6.61 (2H, s, o-H (3,5-Lut(H)), 4.96 (1H, s, NC(CH3)CH), 3.52 (2H, s, CH2), 3.30 (4H, m, CH(CH3)2), 3.13 (2H, m, CH(CH3)2), 1.73 (12H, s, m-CH3 (3,5-Lut and 3,5-Lut(H)), 1.71 (6H, s, NC(CH3)CH), 1.24 (12H, d, JHH = 6 Hz, CH(CH3)2), 1.03 (12H, d, JHH = 6 Hz, CH(CH3)2), 0.78 (12H, d, JHH = 6 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.3 (NC(CH3)CH), 158.4 (o-C (3,5-Lut), 147.1 (o-C (3,5-Lut(H)), 145.7, 141.7, 140.7, 133.4, 125.5, 123.5, 121.3, 120.8. 94.5 (NC(CH3)CH), 61.2 (CH2), 32.0 (NCH(CH3)2), 28.5 (CH(CH3)2), 28.1 (CH(CH3)2), 24.5 (CH(CH3)2), 24.3, (CH(CH3)2), 24.2 (NC(CH3)CH), 23.5 (CH(CH3)2), 23.1 (m-CH3 (3,5-Lut)), 17.9 (m-CH3 (3,5-Lut(H)). Despite repeated attempts, an acceptable elemental analysis could not be obtained for this highly air- and moisture-sensitive compound. HRMS (ESI): calcd for hydrolyzed product [M+Na+]+ C20H28N2NaO m/z 335.45, found 335.2099. Compound 11. A toluene solution of compound V (50 mg, 0.08 mmol) was stirred with MesNCO (13 mg, 0.08 mmol) at room temperature. Concentration to incipient crystallization yielded compound 11 as yellow crystals (43 mg, 66%). Reaction of 30 mg of 3,5Lut(H) complex with 7.4 mg of MesNCO leads to a reaction product at room temperature. 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 8.31 (2H, s, o-H (3,5-Lut)), 7.18−7.06 (6H, m, Ar-H), 7.02 (1H, s, p-H (3,5Lut)), 6.98 (2H, s, m-H (Mes)), 6.57 (2H, s, o-H (3,5Lut(H))), 4.97 (1H, s, NC(CH3)CH), 3.30 (2H, m, CH(CH3)2), 3.28 (2H, s, CH2), 2.94 (2H, m, CH(CH3)2), 1.79 (12H, s, CH3 (3,5-Lut), (3,5-Lut(H))), 1.74 (6H, s, NC(CH3)CH), 1.55 (3H, s, p-CH3 (Mes)), 1.53 (6H, s, o-CH3 (Mes)), 1.17 (12H, d, JHH = 9 Hz, CH(CH3)2), 1.05 (12H, d, JHH = 9 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 169.0 (NC(CH3)CH), 147.7, 146.1, 142.8, 134.9, 133.1, 131.8, 125.2, 123.9, 123.3, 94.6 (NC(CH3) CH), 33.7 (CH2), 28.4 (CH(CH3)2), 27.2, 26.7, 24.7, 24.5, 24.2, 23.7, 23.1, 19.6, 18.4 (CH3 3,5-Lut), 17.8 (CH3 3,5-Lut(H)). Anal. Calcd (found) for C53H71MgN5O: C 77.78 (77.63); H 8.74 (8.85); N 8.56 (8.43). HRMS (ESI): calcd for hydrolyzed product [M]+ C17H22N2O m/z 270.38, found 271.1810; [M+Na+]+ C17H22N2NaO m/z 293.37, found 293.1630. 2597

DOI: 10.1021/om5012374 Organometallics 2015, 34, 2590−2599

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1.24 (12H, d, JHH = 6 Hz, CH(CH3)2), 1.04 (12H, d, JHH = 6 Hz, CH(CH3)2), 0.76 (3H, t, JHH = 6 Hz, NCH2CH3). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 168.7 (NC(CH3)CH), 154.1 (o-CH iQuin), 148.6 (o-CH iQuin), 143.1, 142.9, 136.8, 133.4, 132.7 (NCH), 131.7, 129.0, 126.5, 126.2, 125.2, 124.3, 124.0, 121.7, 106.3 (NCHCH), 94.8 (NC(CH3)CH), 53.0 (NCH2), 42.0 (NCH2CH3), 29.1 (CH(CH 3 ) 2 ), 28.6 (CH(CH 3 ) 2 ), 25.5 (NC(CH 3 )CH), 25.0 (CH(CH3)2), 24.9 (CH(CH3)2), 24.8 (CH(CH3)2), 24.4 (CH(CH3)2), 15.4 (NCH2CH3). Despite repeated attempts, an acceptable elemental analysis could not be obtained for this highly air- and moisture-sensitive compound. Compound 16. A toluene solution of compound VI (330 mg, 0.47 mmol) was stirred with t-BuNCO (89 μL, 0.47 mmol) at room temperature. Concentration to incipient crystallization yielded compound 16 as yellow crystals (40 mg, 43%). 1H NMR (300 MHz, d8-Tol, 300 K) δH (ppm): 7.30−6.98 (20H, m, Ar), 5.86 (2H, s, NCH), 4.94 (2H, s, NC(CH3)CH), 4.12 (4H, s, NCH2), 3.56 (2H, m, CH(CH3)2), 3.35 (2H, m, CH(CH3)2), 3.26 (2H, m, CH(CH3)2), 3.11 (2H, m, CH(CH3)2), 1.82 (6H, d, JHH = 9 Hz, CH(CH3)2), 1.68 (12H, s, NC(CH3)), 1.32 (6H, d, JHH = 6 Hz, CH(CH3)2), 1.30 (18H, s, C(CH3)3), 1.26 (6H, d, JHH = 6 Hz, CH(CH3)2), 1.21 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.90 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.88 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.86 (6H, d, JHH = 6 Hz, CH(CH3)2), 0.53 (6H, d, JHH = 6 Hz, CH(CH3)2). 13C{1H} NMR (75 MHz, d8-Tol, 300 K) δC (ppm): 152.98, 146.37, 143.67, 143.39, 142.35, 135.98, 129.98, 126.96, 126.50, 123.65, 120.27, 95.75 (NC(CH3)CH), 50.54, 32.03 (CH(CH3)2), 29.70 (CH(CH3)2), 28.18 (CH(CH3)2), 27.72 (CH(CH3)2), 25.12 (CH(CH3)2), 24.73 (CH(CH3)2), 24.47 (CH(CH3)2), 24.00 (CH(CH3)2), 23.77 (CH(CH3)2), 23.35 (CH(CH3)2), 23.09 (C(CH3)3), 14.32 (CH(CH3)2). Anal. Calcd (found) for C86H116Mg2N8O2: C 76.94 (76.80); H 8.71 (8.63); N 8.35 (8.20). HRMS (ESI): calcd for hydrolyzed product [M+Na+]+ C14H18N2NaO m/z 252.15, found 253.1317. Compound 17. A toluene solution of compound VI (100 mg, 0.14 mmol) was stirred with AdNCO (25 mg, 0.15 mmol) at room temperature. Concentration to incipient crystallization yielded compound 17 as yellow crystals (35 mg, 33%). 1H NMR (300 MHz, C6D6, 300 K) δH (ppm): 7.43−6.78 (20H, m, Ar), 6.63 (2H, s, NCH), 4.60 (2H, s, NC(CH3)CH), 4.14 (2H, s, NH), 3.54 (4H, s, NCH2), 3.29 (4H, m, CH(CH3)2), 2.94 (4H, m, CH(CH3)2), 1.94 (12H, d, JHH = 9 Hz, CH2CH), 1.56 (12H, s, NC(CH3)), 1.35−1.24 (18H, m, CH2CHCH2), 1.21 (12H, d, JHH = 6 Hz, CH(CH3)2), 1.14 (12H, d, JHH = 6 Hz, CH(CH3)2), 0.90 (12H, d, JHH = 6 Hz, CH(CH3)2), 0.86 (12H, d, JHH = 6 Hz, CH(CH3)2). 13C NMR (75.5 MHz, C6D6, 300 K) δC (ppm): 159.94, 142.70, 125.81, 123.50, 120.21, 97.83 (N(CH3)CH), 43.17 (NCO), 32.03, 30.07 (CH(CH3)2), 28.63 (CH(CH3)2), 24.48 (CH(CH3)2), 23.70 (CH(CH3)2), 23.36 (CH(CH3)2), 23.10 (CH(CH3)2). Anal. Calcd (found) for C98H128MgN8O2: C 78.54 (78.32); H 8.61 (8.50); N 7.48 (7.25). HRMS (ESI): calcd for hydrolyzed product [M+H+]+ C20H25N2O m/z 308.42, found 309.1967. X-ray Crystallography. Data for compounds 1, 12b, 13, 14 and 17 were collected at 150 K on a Nonius KappaCCD diffractometer equipped with an Oxford Cryosystem, using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). Data were processed using the Nonius Software.25 Structure solution, followed by full-matrix leastsquares refinement was performed using the program suite X-SEED except for compound 17, for which the WINGX-1.70 suite of programs was employed.26,27 The asymmetric unit of compound 12b equates to one-quarter of a dimer molecule. Atoms Mg(1), O(1), N(2), C(16), H(16), and C(17) are located on a mirror plane implicit in the space group symmetry. The full molecule is generated via the combination of this symmetry element plus the inversion center proximate to Mg(1). An additional ramification of the high symmetry recorded herein is that, with the exception of C17, all atoms in the adamantane cage are disordered over two sites. In the structure of compound 14 the methyl hydrogens attached to C(1) and C(5) are disordered.

Article

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic information files (CIF) for 1, 12b, 13, 14 and 17. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the EPSRC (UK) for funding. DEDICATION Dedicated to the great inorganic chemist the late Professor Michael F. Lappert FRS.

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REFERENCES

(1) (a) Berg, J. M.; Tymoczko, J. L.; Stryer, L. Biochemistry, 5th ed.; Freeman: New York, 2002. (b) Eisner, U.; Kuthan, J. Chem. Rev. 1972, 72, 1−42. (2) Hantzsch, A. Justus Liebigs Ann. Chem. 1882, 215, 1−82. (3) Wang, N. X.; Zhao, J. Synlett 2007, 2785−2791. (4) (a) Pape, A. R.; Kaliappan, K. P.; Kündig, E. P. Chem. Rev. 2000, 100, 2917−2940. (b) Keay, J. G. Adv. Heterocycl. Chem. 1986, 39, 1− 77. (c) Sulzbach, R. A. J. Organomet. Chem. 1970, 24, 307−314. (d) Ziegler, K.; Zeiser, H. Chem. Ber. 1930, 63, 1847−1851. (e) Armstrong, D. R.; Mulvey, R. E.; Barr, D.; Snaith, R.; Reed, D. J. Organomet. Chem. 1988, 350, 191−205. (f) Clegg, W.; Dunbar, L.; Horsburgh, L.; Mulvey, R. E. Angew. Chem., Int. Ed. 1996, 35, 753− 755. (5) (a) Lansbury, P. T.; Peterson, J. O. J. Am. Chem. Soc. 1963, 85, 2236−2242. (b) Lansbury, P. T.; Peterson, J. O. J. Am. Chem. Soc. 1961, 83, 3537−3538. (c) Lansbury, P. T.; Peterson, J. O. J. Am. Chem. Soc. 1962, 84, 1756−1757. (d) Tanner, D. D.; Yang, C.-M. J. Org. Chem. 1993, 58, 1840−1846. (e) Hensen, K.; Lemke, A.; Stumpf, T.; Bolte, M.; Fleischer, H.; Pulham, C. R.; Gould, R. O.; Harris, S. Inorg. Chem. 1999, 38, 4700−4704. (6) Green, S. P.; Jones, C.; Stasch, A. Angew. Chem., Int. Ed. 2008, 47, 9079−9083. (7) (a) Hill, M. S.; MacDougall, D. J.; Mahon, M. F. Dalton Trans. 2010, 39, 11129−11131. (b) Hill, M. S.; Kociok-Kö hn, G.; MacDougall, G.; Mahon, M. F.; Weetman, C. Dalton Trans. 2011, 40, 12500−12509. See also: (c) Intemann, J.; Lutz, M.; Harder, S. Organometallics 2014, 33, 5722−5729. (8) Arrowsmith, M.; Hill, M. S.; Hadlington, T.; Kociok-Köhn, G.; Weetman, C. Organometallics 2011, 30, 5556−5559. (9) Hao, L.; Harrod, J. F.; Lebuis, A.-M.; Mu, Y.; Shu, R.; Samuel, E.; Woo, H.-G. Angew. Chem., Int. Ed. 1998, 37, 3126−3129. (10) (a) Gutsulyak, D. V.; van der Est, A.; Nikonov, G. I. Angew. Chem., Int. Ed. 2011, 50, 1384−1387. (b) Osakada, K. Angew. Chem., Int. Ed. 2011, 50, 3845−3846. (11) Dudnik, A. S.; Weidner, V. L.; Motta, A.; Delferro, M.; Marks, T. J. Nat. Chem. 2014, 6, 1100−1107. (12) (a) Arrowsmith, M.; Hill, M. S. Alkaline Earth Chemistry: Applications in Catalysis, Comprehensive Inorganic Chemistry II; Chivers, T., Ed.; Elsevier, 2013; Vol. 1, pp 1189−1216. (b) Crimmin, M. R.; Hill, M. S. Top. Organomet. Chem. 2013, 45, 191−241. (13) For a review, see: Diaconescu, P. L. Acc. Chem. Res. 2010, 43, 1352−1363. (14) See, for example: Chang, C.-C.; Chen, J.-H.; Srinivas, B.; Chiang, M. Y.; Lee, G.-H.; Peng, S. M. Organometallics 1997, 16, 4980−4984. 2598

DOI: 10.1021/om5012374 Organometallics 2015, 34, 2590−2599

Article

Organometallics (15) (a) Hernán-Gómez, A.; Bradley, T. D.; Kennedy, A. R.; Livingstone, Z.; Robertson, S. D.; Hevia, E. Chem. Commun. 2013, 49, 8659−8661. (b) Chisholm, M. H.; Huffman, J. C.; Phomphrai, K. J. Chem. Soc., Dalton Trans. 2001, 222−224. (16) Fedushkin, I. L.; Skatova, A. A.; Fukin, G. K.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2005, 2332−2338. (17) Chang, C.-C.; Srinivas, B.; Wu, M. L.; Chiang, W. H.; Chiang, M. Y.; Hsiung, C. S. Organometallics 1995, 14, 5150−5159. (18) Chang, C.-C.; Ameerunisha, M. S. Coord. Chem. Rev. 1999, 189, 199−278 and references therein. (19) Connon, S. J. Org. Biomol. Chem. 2007, 5, 3407−3417. (20) Miller, K. L.; Williams, B. N.; Benitez, D.; Carver, C. T.; Ogilby, K. R.; Tkatchouk, E.; Goddard, W. A., III; Diaconescu, P. L. J. Am. Chem. Soc. 2010, 132, 342−355. (21) Schwetlick, K.; Noak, R.; Stebner, F. J. Chem. Soc., Perkin Trans. 2 1994, 599−608. (22) Rowley, C. N.; Ong, T.-G.; Priem, J.; Woo, T. K.; Richeson, D. S. Inorg. Chem. 2008, 47, 9660−9668. (23) Matsubara, R.; Kobayashi, S. Acc. Chem. Res. 2008, 41, 292−301. (24) Stork, G.; Terrell, R.; Szmuszkovicz, J. J. Am. Chem. Soc. 1954, 76, 2029−2030. (25) DENZO-SCALEPACK: Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276: Macromolecular Crystallography, part A; Carter, C. W., Jr.; Sweet, R. M., Eds.; Academic Press, 1997; pp 307−326. (26) Barbour, L. J. X-Seed - A software tool for supramolecular crystallography. J. Supramol. Chem. 2001, 1, 189−191. (27) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838.

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DOI: 10.1021/om5012374 Organometallics 2015, 34, 2590−2599