Syntheses of Four-Coordinate Nickel(II)-Phosphine Compounds and a

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Syntheses of Four-Coordinate Nickel(II)-Phosphine Compounds and a Rapid Suzuki−Miyaura Cross-Coupling Reaction for Short Laboratory Sessions Jason Cooke* Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada

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S Supporting Information *

ABSTRACT: [NiBr2(PPh3)2] and [NiBr2(dppe)] are prepared from nickel bromide hydrate and phosphine. These brightly colored coordination compounds are then converted into the related organometallic compounds trans-[NiBr(Mes)(PPh3)2] and [NiBr(Mes)(dppe)] (Mes = 2,4,6-Me3C6H2) by reaction with the Grignard reagent MesMgBr. Characterization of the compounds is accomplished by a combination of UV−vis and multinuclear NMR spectroscopies. [NiBr(Mes)(dppe)] is a highly active precatalyst for the Suzuki− Miyaura cross-coupling of 4′-bromoacetophenone and phenylboronic acid. The catalytic reaction is complete in as little as 15−20 min with only a 1 mol % precatalyst loading, and the reaction can be carried out in air. Results are assessed by 1H NMR spectroscopy, or the solid 4-acetylbiphenyl product can be isolated following aqueous workup and recrystallization. The experiments are flexible and accommodate a variety of laboratory schedules and student skill levels. Each experimental component has been designed to be completed within a 3 h laboratory period. KEYWORDS: Second-Year Undergraduate, Inorganic Chemistry, Laboratory Instruction, Hands-On Learning/Manipulatives, Catalysis, Coordination Compounds, NMR Spectroscopy, Organometallics, Synthesis, UV−Vis Spectroscopy were first prepared almost 60 years ago,8 and similar species are often proposed as intermediates in Suzuki−Miyaura reactions.4,5,9 Most isolable compounds demonstrate the “ortho effect” whereby the presence of a reasonably sized substituent in the 2 and/or 6 positions of the aryl ring acts as a form of protection against further reactivity of the nickel center, increasing the thermodynamic stability of the product.8,10,11 A little over a decade ago, Martinez and co-workers described an advanced experiment for the preparation of trans-[NiX(Ar)(PPh3)2] compounds (X = Cl, Br; Ar = substituted aryl).10 In one case, [NiCl2(PPh3)2] was reacted with the student-prepared Grignard reagent MesMgBr (Mes = 2,4,6-Me3C6H2). The relative ease of preparing [NiBr2L2] (L2 = (PPh3)2, 1a or Ph2PCH2CH2PPh2 = dppe, 1b),12 and the commercial availability of relatively inexpensive MesMgBr in THF solution, made an extension of Martinez’s experiment to preparing [NiBr(Mes)L2] (L2 = (PPh3)2, 2a, or dppe, 2b) desirable to investigate. In particular, it would enable students to prepare an organometallic compound from a transition metal coordination

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ickel has a vast and varied chemistry and is often featured in coursework on transition metal chemistry. Although a range of oxidation states from 0 through +4 are known, the +2 oxidation state is the most commonly encountered.1 Coordination compounds of the type [NiX2L2] (X = monoanion, L = phosphine) have been prepared in undergraduate experiments in inorganic chemistry for decades,2 having first appeared in the research literature more than 80 years ago.3 The advantages these compounds present for the student of inorganic chemistry are their relative ease of preparation and their ability to demonstrate fundamental characteristics of coordination compounds. More recently, these types of nickel(II) compounds have been used in a variety of homogeneous catalytic reactions,4 including the important carbon−carbon bond-forming Suzuki−Miyaura cross-coupling reaction.5 The involvement of nickel compounds in the latter process has drawn the interest of chemical educators due to the importance of the Suzuki−Miyaura reaction as a critical synthetic tool in fundamental research and a variety of chemical industries.6 Recently, a “chemical renaissance” of sorts has occurred, wherein a new and exciting branch of rational precatalyst design has been developed for [NiX(Ar)L2] compounds (X = Cl or Br, Ar = substituted aryl, L = N- or Pdonor ligands).7 Variants of the [NiX(Ar)L2] compound type © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: November 16, 2018 Revised: June 24, 2019

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DOI: 10.1021/acs.jchemed.8b00945 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

Scheme 1. Summary of the Various Syntheses of Nickel(II)-Phosphine Compounds Possible in the Experiment

a

Times are for the full procedure, excluding spectroscopic characterization. bCompounds 1a,b must be dried in vacuo or in a drying oven before use in B and D. cIncludes 30 min for glassware assembly and nitrogen purging; if done in air, subtract 30 min. dIncludes 30 min to standardize the Grignard reagent; if an instructor does this step, subtract 30 min.

create flexible multiweek experiments, with each component being less than 3 h in duration (Scheme 1). Although all work can be performed in air, reactions B, D, and E are best done under a nitrogen atmosphere and introduce important techniques for the inorganic chemistry student to learn and practice.6b

compound, and it provides a link between the two topics. Finally, investigating the reactivity of 2a,b in a model Suzuki− Miyaura cross-coupling reaction would provide an extension to organometallic catalysis. The use of purchased MesMgBr would also trim ∼1.5−2 h from Martinez’s protocol and allow the synthesis to be easily completed within a 3 h laboratory period. Many institutions adopt a “fixed-length lab period once per week” approach to laboratory instruction. In such cases, overnight refluxes, multiday stirring periods, and other lengthy procedures that are routine operations in research laboratories cannot be accommodated in teaching laboratories for logistical reasons. Thus, it can be challenging to develop interesting student laboratory experiences that are compatible with traditional scheduling constraints. The experiments described herein have been designed so that each component can be completed within a single 3 h laboratory session. The primary learning objectives (LO) of the experiment are to

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The four nickel compounds are active precatalysts for the Suzuki−Miyaura reaction between 4′-bromoacetophenone and phenylboronic acid (reaction F, eq 1), which is often used by researchers as a “screening run” to test the efficacy of newly designed precatalysts or catalytic reaction conditions.15 Reaction F has been studied under various conditions and has been optimized, with compound 2b proving to be the most active catalyst precursor. Reaction F can be performed on a smaller scale with 1H NMR analysis of the reaction mixture, or it can be performed as a full synthesis with conventional isolation of the 4-acetylbiphenyl product (3). One advantage of the chosen catalytic reaction is that the product is a solid and, therefore, can be purified by recrystallization rather than column chromatography as is commonly required in other systems. Full experimental details are provided in the Supporting Information (SI).

• allow for an increasing level of sophistication of experimental and characterization techniques as students move from a fairly simple preparation of 1a,b to the more demanding syntheses of 2a,b (LO1); • illustrate fundamental concepts such as formation of different stereoisomers, the influence of monodentate versus bidentate ligands, and the use of modern spectroscopic methods in the investigation of these topics (LO2); • have students prepare a rationally designed catalyst precursor and subsequently use it to good effect in a Suzuki−Miyaura cross-coupling reaction (LO3); • consider that catalyst precursors “obtained from a bottle” may not be the same as the catalytically active species (LO4).

Implementation and Scheduling Options

The experiments have been carried out in a second-year undergraduate inorganic chemistry laboratory course and an advanced inorganic chemistry laboratory course over the past 7−10 years. Class sizes ranged from 24 to 135 students, and individual lab section sizes varied from 8 to 12 students. The experiment could potentially last 5 or 6 weeks if all four nickel compounds were prepared and one Suzuki−Miyaura crosscoupling reaction was done with full workup. Alternatives to offer shorter 2−4 week variants and to have the experiment

OVERVIEW OF THE EXPERIMENT The preparations of 1a,b are modifications of existing procedures.2c,12 Additional inspiration from the work of Seidel13 and Klein14 allowed optimization of the syntheses of 2a,b to B




synthesis of 2b is even more efficient, with yields often exceeding 85%. The consistently higher yields of the dppe compounds (1b and 2b) compared to the PPh3 analogues (1a and 2a) are presumably due to the chelating, stabilizing nature of the bidentate phosphine. In contrast, the lability of the monodentate PPh3 ligands in 2a is readily demonstrated by the mild conditions required for displacement by chelating dppe (reaction E). Compounds 2a and 2b (when prepared by reaction D) crystallize with half an equivalent of THF that is difficult to remove except by drying for 1 week in an oven at 85 °C (additional details are in the SI, pages I6−I7). The four brightly colored nickel compounds are all amenable to characterization by UV−vis spectroscopy in CH2Cl2 solution (SI, Figures I1−I4). Compound 1a shows two peaks at 585 and 911 nm, with extinction coefficients of 1.9 × 101 and 2.5 × 101 cm−1 M−1, as is typically seen for tetrahedral nickel(II) compounds.2a,17 On the other hand, compounds 1b, 2a, and 2b show a single prominent peak to shorter wavelength (477, 447, and 425 nm, respectively) with larger extinction coefficients (1.6 × 103, 4.3 × 102, 1.6 × 103 cm−1 M−1, respectively) in keeping with a square planar geometry.12,17b The students were provided with criteria for the qualitative differences in the appearance of the UV−vis spectra for tetrahedral and square planar nickel(II) compounds to use as a guide for determining the coordination geometries of 1a,b and 2a,b. Molar extinction coefficients were calculated as a matter of routine. The square planar compounds are diamagnetic and therefore can be further characterized by 1H and 31P{1H} NMR spectroscopy (SI, Figures I5−I11). The simple singlet at 19.40 ppm in the 31P{1H} NMR spectrum of 2a confirms the trans disposition of the phosphine ligands,14 whereas asymmetric 2b displays the anticipated pair of doublets at 52.62 and 31.48 ppm (2JPP = 14.5 Hz).18 The 1H NMR spectra of compounds 2a and 2b show the characteristic peaks for the mesityl and phosphine ligands. In 2a, the mesityl group displays singlets at 5.80 (2H), 2.37 (6H), and 1.90 ppm (3H), along with a broad singlet at 7.5 ppm (12H) and two apparent triplets (J = 7.2 Hz) at 7.30 (6H) and 7.19 ppm (12H) for the protons in the six C6H5 rings. The 1 H NMR spectrum of 2b is more complex owing to the asymmetry of the bidentate phosphine. The mesityl group shows the expected 2:6:1 pattern of singlets at 6.22, 2.38, and 2.03 ppm, but the two upfield signals overlap with the methylene resonances for the dppe ligand, which appear as multiplets at 2.33 and 2.02 ppm. The two pairs of C6H5 rings present as multiplets at 7.99 (4H), 7.46 (6H), 7.35 (6H), and 7.19 ppm (4H). Recording the 1H{31P} NMR spectrum of 2b is beneficial as it reduces the complexity of multiplets for the methylene resonances and introduces an additional spectroscopic technique (see SI, Figure I10). Thus, two triplets (3JHH = 6.8 Hz) are resolved at 2.33 and 2.02 ppm, although the latter remains overlapped with the methyl resonance from the mesityl group.

extend across two courses are described in the SI (pages I3−I4). It is also possible for an instructor to prepare a large batch of 1a,b or 2a for the students to use as a starting material. Different formats exist for Suzuki−Miyaura reaction F. The cross-coupling reaction can be performed as a simple reflux in air, either as a 1H NMR study or as a full synthesis including aqueous workup and recrystallization of compound 3. In the earlier stages of development, students experimented with different reaction conditions and solvents as a team project and also studied the reaction using 2a as the precatalyst. Results were shared for the entire lab section and were subsequently evaluated to gauge the best conditions for the synthesis. Similar approaches could be undertaken by instructors who wish to expose their students to the optimization of catalytic reaction conditions.

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HAZARDS Students should wear appropriate personal protective equipment (PPE) including a lab coat, long pants, closed shoes, safety glasses, and nitrile gloves during all parts of the experiment. All experimental work should be performed in a well-ventilated fume hood. All waste should be managed in accordance with the chemicals’ SDS sheets and local environmental, health, and safety regulations. All chemicals used in this experiment should be treated as being hazardous and/or toxic if ingested. Nickel(II) compounds16 and chloroform-d are irritants and suspected carcinogens; nickel(II) bromide hydrate is toxic to aquatic life. Ethanol, propan-2-ol, and 2-methyl-butan-2-ol are flammable eye irritants; methanol is additionally highly toxic, and skin contact must be avoided. Toluene is highly toxic by ingestion, is flammable, and is a suspected teratogen. Dichloromethane is a toxic liquid that is an eye, skin, and respiratory irritant and is a suspected carcinogen. Diethyl ether is an extremely flammable liquid with a low flash point. Tetrahydrofuran is flammable and is a moderate to severe eye and respiratory irritant. Diethyl ether and tetrahydrofuran have the potential to form explosive peroxides upon prolonged storage. 2Mesityl magnesium bromide solutions in tetrahydrofuran are flammable and corrosive and react violently with water; the mixture is also a suspected carcinogen. Iodine is corrosive and toxic. Triphenylphosphine may cause an allergic skin reaction and may cause damage to the nervous system through prolonged or repeated direct exposure. Anhydrous potassium phosphate is corrosive and is a skin, respiratory, and eye irritant. Phenylboronic acid, 4′-bromoacetophenone, 4-acetylbiphenyl, and 1,2bis(diphenylphosphino)ethane are skin and eye irritants. Celite is an irritant and is hazardous if inhaled. The properties of compounds 1a,b and 2a,b have not been thoroughly studied, and therefore, they should be handled with appropriate caution.

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RESULTS AND DISCUSSION

Synthesis and Spectroscopic Characterization of the Nickel(II)-Phosphine Compounds

Synthesis of 4-Acetylbiphenyl by Suzuki−Miyaura Cross-Coupling

The experiments detailed in Scheme 1 have each been performed a minimum of 30 times, with some (reactions A, B, and C (MeOH/toluene reflux)) having been carried out by over 450 different students to date. The yield of compound 2a is typically 65−85%, which is significantly higher than the ∼10− 20% yields reported for trans-[NiX(Mes)(PPh3)2] (X = mixture of Cl/Br, prepared from [NiCl2(PPh3)2]).10 Additionally, using 1a as the precursor rather than the more common chloro compound2b−e,6b,10 avoids a mixed halide product. The

The optimized conditions for catalytic reaction F were studied by 1H NMR spectroscopy of the solid residue obtained after evaporation of the solvent from the reaction mixtures. Quantitative conversion of starting material to product (3) was seen in 85% of the trials using 1 mol % of 2b (SI, Figure S5). In these cases, the 1H NMR spectrum showed the characteristic pattern for 4-acetylbiphenyl (SI, Figure S4), with the downfield two-proton multiplet at 8.04 ppm and the downfield-shifted C




(trifluoromethyl)biphenyl.6b In both cases, the chelating nature of dppe presumably imparts greater stability to the catalytically active species than does monodentate PPh3.

methyl singlet at 2.64 ppm being especially diagnostic. The remaining students observed 10% or less unreacted 4′bromoacetophenone, which was identified primarily by the presence of its upfield methyl singlet at 2.58 ppm (SI, Figure S3; Figure I12 provides an example of a 1H NMR spectrum for incomplete conversion to 3). When the quantity of 2b was increased to 2 mol %, all students observed quantitative formation of 3. No homocoupled 4,4′-diacetylbiphenyl was detected in any of the reactions. However, student success at achieving high isolated yields of 3 was poorer, with most falling below 50% despite an average 74% recovery of crude product before recrystallization. This can be attributed to student unfamiliarity with the workup technique, as students in these two classes normally have only two terms of previous organic chemistry experience. By comparison, careful instructor checking of the procedure exceeded 95% recovery of anticipated crude product from the reaction mixture and greater than 75% yield of recrystallized material. It is likely that if additional experience with basic organic chemistry manipulations was available, then results in this portion of the experiment would improve. The relatively small scale of the reaction (theoretical yield of 0.30 g for 3) may also play a role; generally, students realize lower isolated yields as reaction scales decrease. It is noteworthy that a nitrogen atmosphere is not necessary for reaction F, which contrasts with many other nickel-catalyzed Suzuki−Miyaura cross-coupling reactions.5,6b,7,9 This satisfies criteria described recently by Jamison relating to the ease of synthesis and activation of ideal nickel precatalysts, and the desire for simple, benchtop catalytic reactions carried out in air.19 Furthermore, it is an important example of an experiment in which students can easily prepare and then subsequently use a molecular catalyst precursor. To date, only one other such undergraduate experiment has been described for nickel, and this example6b requires a logistically challenging overnight reflux under nitrogen. Calculation of the turnover number (TON)6b (eq 2) is commonly done for catalytic reactions. However, students can potentially learn more about the reaction by also calculating the turnover frequency (TOF) (eq 3). TON =

% conversion mol % catalyst

(2)

TOF =

TON time (in h)

(3)

Mechanism of Precatalyst Activation in a Suzuki−Miyaura Cross-Coupling Reaction

It is fairly well established that Suzuki−Miyaura cross-coupling in palladium-catalyzed systems occurs by a two-electron process initiated by oxidative addition of an aryl halide to a Pd(0) species.4,9,20 Although it is thought that a similar mechanism is likely operating for nickel,5,9 other possibilities exist. Fundamental differences exist between nickel and palladium, which include nickel’s more electropositive nature and easier access to radical pathways involving Ni(I) and Ni(III) species.4 Nevertheless, the two-electron M(0)/M(II) mechanism (Scheme 2) is Scheme 2. Generic Two-Electron M(0)/M(II) Catalytic Cycle for Suzuki−Miyaura Cross-Coupling Reactions

a useful model for students as it illustrates several key reactions in organometallic catalysis, namely, oxidative addition (OA), reductive elimination (RE), and transmetalation (TM). Naturally, a very valid question is how the catalytically active LnM species is formed. This question also introduces the concept of a precatalyst, which may be different than the catalytically active species (LnM in Scheme 2). For instance, existing examples of undergraduate experiments utilize Ni(II) precatalysts with the general formulation [NiCl2L2],6a,b for which there is no immediately obvious pathway to form the catalytically active species. Conversely, with appropriate background discussion, students can appreciate that species such as 2a,b can undergo the reactions shown in eq 4.

For fast reactions like F, the determination of TOF can be made more precise by reducing the scale to shorten the induction period to achieve reflux. The calculation of TOF also allows for a more direct comparison with other reactions carried out under the same conditions. For example, the quantitative conversion in eq 1 gives a TON of ∼100 and TOF on the order of ∼300 h−1 when eqs 2 and 3 are applied. This is several orders of magnitude faster than a recent undergraduate experiment where 4-(trifluoromethyl)biphenyl formed in 83−93% yield following overnight reflux under nitrogen using 10% [NiCl2(dppe)].6b These yields correspond to a TON of ∼8−9 and TOF of ∼0.4−0.5 h−1. Thus, students are challenged to consider all three parameters (yield, TON, and TOF) when evaluating the results of a catalytic reaction, as one parameter may not tell the full story. When 2a was used in place of 2b in reaction F, TON and TOF dropped by 65−75%. Similarly, [NiCl2(PPh3)2] was less effective than [NiCl2(dppe)] in catalyzing the formation of 4-

As the techniques are more appropriate for advanced courses, experimental methods for investigating this process are discussed further in the SI (pages I9−I12). Overall Evaluation of Learning Objectives

Students received a positive experience requiring the application of a variety of experimental techniques and characterization methods in a multiweek experiment connecting topics in transition metal coordination chemistry, organometallic chemistry, and catalysis. From an instructor perspective, a variety of approaches were possible with regard to organization and implementation. Successful achievement of the experimental portion of the learning objectives (LO1 and LO3) was evident from the students’ in-lab results. The syntheses of the nickel compounds 1a,b and 2a,b proceeded in good to excellent yield D



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and were readily characterized spectroscopically. The Suzuki− Miyaura cross-coupling reaction provided excellent results in terms of conversion of starting material to product when 2b was used. Many students commented on how little precatalyst was needed in relation to the larger quantities of the other reagents (several students thought they had made a calculation error as the quantity was so small). The students also gained an appreciation for the challenge of turning quantitative in situ conversion into high yields of isolated product and, in some cases, realized that their synthetic techniques would have to be improved. Traditional written laboratory reports were composed and were completed according to student ability. The graders generally reported a high level of competence with the evaluation of experimental results. Evaluation criteria included the correct interpretation and summary of experimental results, especially spectroscopic data. For LO2, the vast majority of students were able to apply the qualitative criteria to assign a tetrahedral or square planar geometry on the basis of the appearance of the UV−vis spectra. When misunderstandings occurred, the most frequent was presuming that all compounds had a common square planar geometry, perhaps as a consequence of having more lecture-based experience with Pt(II) compounds where this is true. Most students were able correctly calculate extinction coefficients using Beer’s law, although some made calculation errors when determining the solution concentration. The singlet appearance of the 31P NMR spectrum of 2a was readily connected to its adoption of a trans coordination geometry, and the simple AX appearance of the 31P NMR spectrum of 2b was also well-understood, with the most common shortcoming being calculation errors in the determination of 2JPP. The increased complexity of the 1H NMR spectra provided a greater challenge, and the graders reported a wider range of responses according to individual student analytical skills. For the Suzuki−Miyaura cross-coupling reaction (LOs 3 and 4), all students were able to correctly identify that the reaction proceeded to give high yields of 3 on the basis of in situ 1H NMR spectroscopy and most correctly used eqs 2 and 3 to calculate TON and TOF. The more advanced concepts such as consideration of the catalytic cycle and the activation of the precatalyst presented a challenge, and accordingly resulted in the widest range of comprehension. This afforded opportunities to enhance student learning through discussion of the more complicated concepts. Students who had a good understanding of the three fundamental steps of the catalytic cycle (OA, RE, and TM in Scheme 2) tended to be able to predict the mechanism of precatalyst activation in eq 4, whereas those who struggled with the catalytic cycle understandably were less able to rationalize the latter process.


ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00945. Instructor notes (details for organization and implementation, potential extensions for advanced courses, representative spectra, and other experimental results) (PDF, DOCX) Detailed materials for students (background information, experimental procedures, and prelab and postlab questions) (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jason Cooke: 0000-0002-1847-5966 Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS The Department of Chemistry at the University of Alberta is thanked for funding. The efforts of the undergraduate students who have successfully completed various iterations of the experiment are gratefully acknowledged, as are the helpful suggestions of various graduate teaching assistants. Jeremy John, Michael Slaney, and Chem 299 (Research Opportunity Program in Chemistry) students Chun Yan Xie, Simran Gulati, and Minh Tang Duc Hoang are thanked for testing various procedures. Mark “NMark” Miskolzie and Nupur Dubral are gratefully acknowledged for the countless NMR spectra obtained, as is Jing Zheng for her expertise with GC-MS. The reviewers are thanked for their helpful suggestions.

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REFERENCES

(1) (a) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry, 6th ed.; Wiley: New York, 1999; pp 835−846. (b) Housecroft, C. E.; Sharpe, A. G. Inorganic Chemistry, 4th ed.; Pearson Education: Harlow, England, 2012; pp 761−764. (2) (a) Eagle, C. T.; Walmsley, F. Preparation and Characterization of Two Nickel(II) Complexes. J. Chem. Educ. 1991, 68 (4), 336−337. (b) Szafran, Z.; Pike, R. M.; Singh, M. M. Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience; Wiley: New York, 1991; pp 257−260. (c) Parkin, I. P. Nickel Dihalide Phosphine Complexes. In Inorganic Experiments, 3rd ed.; Woolins, J. D., Ed.; VCH: New York, 2010; pp 120−123. (d) Young, C. B. Nickel-Catalysed Cross-Coupling of Alkylmagnesium with Haloarene. In Inorganic Experiments, 3rd ed.; Woolins, J. D., Ed.; VCH: New York, 2010; pp 201−204. (e) Girolami, G. S.; Rauchfuss, T. B.; Angelici, R. J. Synthesis and Technique in Inorganic Chemistry, 3rd ed.; University Science Books: Sausalito CA, 1999; p 90. (3) (a) For the first report of the synthesis of [NiX2L2] (X = monoanion, L = phosphine) compounds, see: Jensen, K. A. Zur Stereochemie des koordinativ vierwertigen Nickels. Z. Anorg. Allg. Chem. 1936, 229 (3), 265−281. (b) For a review of early [NiX2L2] (X = monoanion, L = phosphine) chemistry, see: Booth, G. Complexes of the Transition Metals With Phosphines, Arsines and Stibines. Adv. Inorg. Chem. Radiochem. 1964, 6, 1−69. (4) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous catalysis. Nature 2014, 509, 299−309. (5) Han, F.-S. Transition-metal-catalyzed Suzuki-Miyaura crosscoupling reactions: a remarkable advance from palladium to nickel catalysts. Chem. Soc. Rev. 2013, 42, 5270−5298.

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CONCLUSION A flexible experiment has been described for the synthesis of four nickel(II)-phosphine compounds, two of which are more traditional coordination compounds and two of which are organometallic complexes. One of the organonickel compounds was highly active in a Suzuki−Miyaura cross-coupling reaction, which is of great relevance to modern organic synthesis and specifically to the role played by organometallic compounds in catalysis. A variety of different approaches to the organization and content of the experiments was presented, with an important criterion being that each component could be completed within a 3 h laboratory period. E




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Syntheses of Four-Coordinate Nickel(II)-Phosphine Compounds and a

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