public static IEnumerable<T[]> ToPairs<T>(this IEnumerable<T> sequence)
{
	if (sequence == null) throw new ArgumentNullException("sequence");
	T first = default(T);
	bool haveFirst = false;
	foreach(var item in sequence)
	{
		if (haveFirst)
		{
			yield return new[] { first, item };
			haveFirst = false;
		}
		else
		{
			first = item;
			haveFirst = true;
		}
	}
	if (haveFirst)
	{
		yield return new[] { first };
	}
}

private IEnumerable<int[]> ToPairs(int[] values)
{
	if (values == null) yield break;
	for (int i = 0; i + 1 < values.Length; i += 2)
	{
		yield return new[] { values[i], values[i + 1] };
	}
	if (values.Length % 2 == 1)
	{
		yield return new[] { values[values.Length - 1] };
	}
}

var list = Enumerable.Range(1, 12).ToList();
const int numberOfItems = 5;
var listOfGroups =
  list
    .Take(list.Count / numberOfItems)
    .Select((x, i) => list.GetRange(i * numberOfItems, numberOfItems));