The commonplace reaction of a ketone with a Grignard reagent involves the oxygen acting as a nucleophile ... towards the magnesium.

The view from the other side

Yes, the negatively polarized carbon gets all the headlines as a nucleophile, as this is the function that ends up in the alcohol that we identify as the product after workup. The magnesium literally just comes out in the wash as a salt formed from the original halide in the Grignard reagent and the acid used in the workup.

Yet upon further review the magnesium, at the other end of that polar bond with carbon, is also there, and with its fairly high positive charge density it acts as an ekecttophile. In so doing it contributes to the polarization of the carbonyl group and thus ultimately supports the nucleophilic attack on the carbonyl carbon:

$\ce{\color{blue}{C}H3\color{brown}{Mg}Br + CH3\color{brown}{C}(=\color{blue}{O})CH3 -> CH3-\color{brown}{C}(\color{blue}{O}\color{brown}{Mg}Br)(\color{blue}{C}H3)-CH3}$

(Blue = nucleophile, brown = electrophile)

The commonplace reaction of a ketone with a Grignard reagent involves the oxygen acting as a nucleophile ... towards the magnesium.

The view from the other side

Yes, the negatively polarized carbon gets all the headlines as a nucleophile, as this is the function that ends up in the alcohol that we identify as the product after workup. The magnesium literally just comes out in the wash as a salt formed from the original halide in the Grignard reagent and the acid used in the workup.

Yet upon further review the magnesium, at the other end of that polar bond with carbon, is also there, and with its fairly high positive charge density it acts as an electrophile towards the carbonyl oxygen. The resulting addition of magnesium to oxygen contributes to the polarization of the carbonyl group and thus ultimately supports the nucleophilic attack on the carbonyl carbon:

$\ce{\color{blue}{C}H3\color{brown}{Mg}Br + CH3\color{brown}{C}(=\color{blue}{O})CH3 -> CH3-\color{brown}{C}(\color{blue}{O}\color{brown}{Mg}Br)(\color{blue}{C}H3)-CH3}$

(Blue = nucleophile, brown = electrophile)

The commonplace reaction of a ketone with a Grignard reagent involves the oxygen acting as a nucleophile ... towards the magnesium.

The view from the other side

Yes, the negatively polarized carbon gets all the headlines as a nucleophile, as this is the function that ends up in the alcohol that we identify as the product after workup. The magnesium literally just comes out in the wash as a salt formed from the original halide in the Grignard reagent and the acid used in the workup.

Yet upon further review the magnesium, at the other end of that polar bond with carbon, is also there, and with its fairly high positive charge density it acts as an ekecttophile. In so doing it contributes to the polarization of the carbonyl group and thus ultimately supports the nucleophilic attack on the carbonyl carbon:

$\ce{\color{blue}{C}H3\color{brown}{Mg}Br + CH3\color{brown}{C}(=\color{blue}{O})CH3 -> CH3-\color{brown}{C}(-\color{blue}{O}-\color{brown}{Mg}Br)(\color{blue{C}H3)-CH3}$

(Blue = nucleophile, brown = electrophile)

The commonplace reaction of a ketone with a Grignard reagent involves the oxygen acting as a nucleophile ... towards the magnesium.

The view from the other side

Yes, the negatively polarized carbon gets all the headlines as a nucleophile, as this is the function that ends up in the alcohol that we identify as the product after workup. The magnesium literally just comes out in the wash as a salt formed from the original halide in the Grignard reagent and the acid used in the workup.

Yet upon further review the magnesium, at the other end of that polar bond with carbon, is also there, and with its fairly high positive charge density it acts as an ekecttophile. In so doing it contributes to the polarization of the carbonyl group and thus ultimately supports the nucleophilic attack on the carbonyl carbon:

$\ce{\color{blue}{C}H3\color{brown}{Mg}Br + CH3\color{brown}{C}(=\color{blue}{O})CH3 -> CH3-\color{brown}{C}(\color{blue}{O}\color{brown}{Mg}Br)(\color{blue}{C}H3)-CH3}$

(Blue = nucleophile, brown = electrophile)